Hans in Australia on the bike - Joint Australian AI 07

Weblog in English for the participants to the Joint Australian AI conference in Gold Coast, December 2007, where this tour, for that purpose a 'Logic in Australia' bikeride, has ended with a keynote lecture. And there are photos (with Dutch subscripts). Note that this trip is also a charity drive around Australia by bicycle for the (Dutch) refugee students fund UAF: donation page . For the charity drive there is a companion weblog in Dutch , with different content.

Brisbane - Cairns

The main idea is to bike from Brisbane to Gold Coast indirectly, not following the coast and highway 1 clockwise, but counterclockwise. This should take about half a year, but given that I have to take up a job in France by December I was advised by my colleagues there to speed up a bit and bike faster, so that it would take only five months. We will see... I anticipate some busrides ahead. Anyway, the first leg was from Brisbane to Cairns. Ah - I should not forget to mention that I will be visiting various departments and academics along the road, and give seminars and stuff.

The start of the trip was really the University of Queensland, where I was invited for a seminar by my dear friend Guido Governatori - not incidentally heavily involved in the organization of AI 07 in Goldcoast. I share his interest in modal logics, e.g. Guido also organized the very successful (at least locationwise: it took place in Noosa) AiML conference in 2006: Advances in Modal Logic. Apart from his work in modal logic he appears to have separate existences as a database researcher and is also into e-commerce - a prolific publisher by any standard. Well, praising your friends is one thing, but it paid off: he took me and my bike to the outskirts of Brisbane, so that I could avoid the horrible city traffic. From there on one goes quickly into very deserted areas, the second night I was already forced to camp in a small township called Woolooga. It consisted of one hotel and one shop and a couple of farms. The hotel owner certainly surprised me by, halfway during a chat, going outside for a smoke. As this was the law. It was only him, me, and nobody around for 50 k.... But this is Australia: if it is the law, you have to obey it!

There were various other parts of Australian life I had to get used to. I've been here before, but not frequently, am a half-Kiwi by now, but am originally Dutch. I was already acquainted with the wonders you can accomplish by merely announcing the mantra 'vee bee' in bars. But hereabouts in Queensland there were other beers around too that I did not know well how to pronounce. Well, the four XXXX were clearly enough. But what to say in such a case? A quadruple X please? That was probably a hilarious giveaway for a true foreigner. Seemed though the subscript Castlemaine came with it quite a bit. Let's try that instead. "Sorry mate, we run out of that. Can I get you a asdqwerqas instead?" Sure. I still don't know what it was, but certainly drinkable.

Various other troubles keep coming up... Australians, like everyone around the world, like making up paraphrases of the mens and womens toilet distinction. Cocks and hens, something clearly enough, if I remember it well, resembling male koalas and female koalas, etc. There is a tendency to call these retreats male and female toilets, which I still find funny (maybe it's my highschool English: the toilet itself isn't male, right? It's for males). Now the one thing troubling me currently is the mangoes / no-mangoes distinction. So which of these is for men? Unlike oranges, which would be fairly clear to me, there is a number of things resembling mangoes on human bodies, to my knowledge or rather observation. Could some Australian help me out please? I'm still waiting to see nuts / no-nuts somewhere.

Well, enough of that. The riding goes fairly well, given that there's a stable southerly wind for weeks on end. I was nearly blown from Brisbane to Cairns. The big trucks 'help' too, they tend to pass you with 20 cm distance at high speed, and such you in. This you have to resist my holding tight to the handlebar, but it also speeds you up considerable, so a convoy of five or more gives you a real push. Some things I really don't like very much. Actually all these cars and trucks passing you narrowly all the time is pretty dangerous already. But trucks coming from the other direction and overtaking other trucks while you ride towards them (on a two-lane road), I find plain madness. Still, most traffic will do just that and ignore you, even if you are driving towards them. What I don't like much either are people throwing glass bottles at me while passing, aiming for just in front of the bike. Presumably hoping to cause me a flat tyre. But there is also a substantial risks of high-velocity shards of glass slicing your legs, I've read some stories in the Otago Daily Times on such occurrences.

I am currently at James Cook University in Cairns, as a guest of Nicola Bidwell in the School of Maths, Physics, and Information Technology. Nicola runs a line of research in information acquisition, use and communication also related to applications in computer games. My interest in designing non-computer card games and related games overlaps with hers. This JCU campus is quite fabulously located almost in the middle of a rainforest. It takes half an hour to bus to town - Australian Unis have this habit of not being located in the towns that you associate them with, or like on the extreme outskirts of town. Where I'm noisily accommodated in something called international backpackers hostel, in a closed humid cubicle right next to the night markets... I have terribly efficient earplugs which serve me well, and sleep like a rose. Well, a humid rose.

Cliffhanger: the next leg of the trip will be from Cairns to Darwin, where I will visit Charles Darwin University. The uncertainty of this leg is the number 1 highway that is partly unsealed halfway in between. It is currently unclear if it is wise to proceed there by myself. Next update, in about a month...

And to conclude: a logic puzzle, of course! Each trip story will be accompanied by one riddle. Ask me for solutions at AI 07 in Goldcoast, later this year. The first riddle is:

Cairns - Darwin

From Cairns to Darwin promised to be interesting because of restricted water availability and a long stretch of unsealed road. The first was easy to overcome, the second less so. From Cairns you rise up straightaway to the Atherton Tablelands where it is immediately drier and a lot colder. Quite pleasant, actually. Also, a familiar landscape started to form around me while paddling forth, consisting of red earth, gum trees, lots of dry grass and termite heaps. Australia as I knew it from the pictures but as I had not actually seen yet in real life! Every next town was smaller than the previous one and the distances between towns became larger. Ravenshoe, Georgetown, Croydon, Normanton. Traffic was a lot, really a lot, scarcer than on the Bruce Highway - the number one on the eastcoast. This number one highway is called the Carpentaria Highway. Once you are about 150 km from Cairns it becomes a single lane road. So far, sealed.

Single lane roads are of great interest both to epistemic logicians and game theorists.

Logicians use it as a standard example to explain the concept of common knowledge. Suppose you drive a car, not a bike. Another car comes towards you. Suppose you were uncertain whether that driver knows that we are in the Australian and not in the American desert. (Out of this world, sure, but... Well, let me say no more. That's what logicians are.) He might swerve to the right instead of to the left to avoid you. You however swerve to the left. Bang! So, better slow down. Suppose you know that he knows that one should swerve to the left, but that you don't know if he knows that you know that. You might still slow down, but maybe slightly less so than in the previous scenario... If you know that he knows that you know and so on to infinity, this is common knowledge. Enough of this, or I won't stop talking about this.

Game theorist do other things with single lane roads: they play the game of chicken. This is at stake on the Carpentaria Highway! The classic game of chicken ('do I chicken out or not') is as follows: two cars approach each other at high speed on a single lane road. The chicken driver (chicken/cooperate strategy) veers to the side of the road and lets the other pass. The non-chicken driver, tough guy (dare/defect strategy), does not veer to the side of the road. Then you 'win', from the guy who chickens out. If both chicken out, you both lose a bit, no problem. If both are tough, bang! Again. Big loss. In a typical strategic form, for players A (row) and B (column), with strategies D (defect, or, in this context 'dare') and C (cooperate, or, in this context 'chicken'):

D (0,0) (4,2)
C (2,4) (2,2)

As known, the Nash equilibria are (D,C) and (C,D). This is going to be boring. Well, maybe not: consider a variation on this scenario where we do not have two cars approaching each other but Hans on the bike and some other, approaching, traffic, on this one-lane Australian Outback road. Our first scenario is where Hans (H) meets a road train (R).

This is my payoff matrix for Hans meeting a road truck on a single lane outback highway:

D (0,4) (4,2)
C (2,4) (2,2)

In other words, or rather, in words: to the road train (just talking about speed and immediate consequences and satisfaction) I am not more than a fly hitting the windscreen, and my choices are irrelevant to his. It's merely that he loses a bit by reducing speed, and gets a reward of 2 instead of 4. Somewhat differently, from my point of view, I still seem to have a chance for a reward of 4 in case the road train from some irrational point of view decides to swerve off the road, but, yeah, what reason do I have to assume that? The road train has a dominant strategy to 'dare', i.e. stay on the road, and when we eliminate the dominated column my dominant strategy is to swerve off the road, to 'chicken'. And that's it: the equilibrium here is (C,D). Only.

This is also not very interesting. But here comes the nice part: Hans (H) against the caravan (V). Australian caravan drivers - well, in this part of the year, in Northern Queensland - are typically pensioners going North to catch the sun and warm winter climate. They are all desperate not to go with their caravan off the road because it's such an expensive caravan and the bearings are so sensible to damage and these stupid pushbikes shouldn't be allowed on the road anyway, etc. But, a bicycle and a car, or a bicycle and a caravan, can pass each other safely on a one-lane road as long as both the bicycle and the caravan stay to the side of the lane - one can call this the scenario where swerving is not necessary and both dare. Now the thing is, that I know this, but the caravan driver may not know that, and may think that we would then clash. In other words, I know that the payoff matrix is as follows:

D (4,4) (4,2)
C (2,4) (2,2)

But the caravan driver may well think that is is the normal chicken matrix with payoff (0,0) for (D,D) - as above, the first table. Although strictly it may rather be an incomplete game, it seems to make sense to model this as an imperfect information game where the participants cannot distinguish between two different (D,D) outcomes - or, more interesting again, have a different perception of this outcome. As in this scenario where I can distinguish them.
I play this game repeatly, twenty times a day. I have become an expert and dare most of the time. Also, I can do last-second escapes off the road and avoid the (0,0) scenario if really necessary. For road trains you always get off straightaway because you don't want to annoy these people who have to make a living of driving through Australia. But as you can now imagine I'm occasionally annoying these caravan drivers no end.

It is also the case that if I stay on the road and the caravan gets off the road I in fact still lose a bit, because of the dust and grit flying through the air towards me. I'd much rather have my smaller opponents stay on their one lane. So from that perspective I should then gain even more than the 4 in the (4,2) outcome for (D,C) - where the caravan gets off the road. So then we should not have (4,4) but (5,5), say. And then one could maximize on politeness and the good feeling of getting off the road for other cars, even if not strictly necessary. I do that too.... Well, enough games.

Back to the real road. The Carpentaria Highway first brings you from Cairns to Normanton. Then comes the scary bit, from Normanton to Borroloola is over an unsealed road. A stretch of 700 to 800 km. The first day went from Normanton to Burketown. Well, I now know the meaning - not being a native speaker - of corrugated road. That's those terrible waves or ribbles on an unsealed road surface that make driving in cars unpleasant but bike-riding with narrow tyres and bums on small saddles plain hell. And these outback roads are just terrible. I had a flat tyre quickly. And lost some bits and pieces of my packs too that were just jittering off their attachments. And got a bit thirsty. That part was not so bad, because here in the far North the rivers weren't actually dry and you could fill your water bottles occasionally without any problems. I was a bit unsure about all this crocodile risk business so I always carefully looked right and left and in front of me before leaning over on the river banks and filling my bottles from the stream. In Burketown bad news, both roadhouse further down the road towards Borroloola were closed, for lack of seasonal labourers willing to do the job. Apparently, everybody goes down to the mines at Mount Isa, where pay is much better. Aye, so that's 500 plus without anything and corrugated roads all over and - didn't tell you that yet - sometimes it was just loose sand which bogged you down straightaway so you had to walk.

Well, a day into that I was passed by a friendly Australian couple who first offered me water and then offered me a lift, from near Hells Gate Roadhouse where I met them, to where sealed roads resume: Borroloola. Heaven! From there, it was another five days to Katherine. Through thrilling places like the Heartbreak Hotel (disappointing) and Daly Waters (not so). At the time that surely was the hottest area in all Australia. Darwin is degrees cooler than the Katherine area. Katherine turned out to be the first reasonable internet connection since Cairns. I had not realized that. So, to be more or less explicit: if you do the 2000+ km from Cairns to Darwin the first internet is at the end of the trip. Normanton had a library with a 4-second-per-typed-character-connection, always a bit of a bore. Daly Waters had a computer with a 2-dollar coin operation. Ah, unfortunately off-line right now. Ah, unfortunately off-line 2 hours later too. Ah, there we go again. The next town had a village library but as it was Saturday this was closed. And then Katherine.

I am now in Darwin, as a guest of John Haynes, in the Department of Information Technology at Charles Darwin University. I was also extremely pleased to make the acquaintance of Ramakoti Sadananda, to whom I was introduced by way of Guido. Sadananda is the local chair of the upcoming PRIMA conference, in Bangkok, which will be held at the Rangsit University where he is vice-president of research (one of a long, long list of positions and honours). He has an adjunct position at the department here, gave me much of his time, and we mused on a wide range of issues of general and philosophical interest.
And I've just given my next seminar, on logic puzzles again. (Not 'of course' but indeed I gave the same one in Cairns, and in Brisbane.) This was quite interesting because John has a different approach to solve such riddles coined as perspectival thinking , which promises to explain the role that direct intuition and jumps of the imagination play in the way humans solve such problems - and he as well wrote a book on this topic. Charles Darwin University is lying in fabulous surroundings, lush trees and birds everywhere. This seems to be an Australian constant. Good coffee too. And architecturally this university is also quite interesting. CDU is in fact split over different campuses - there is an Alice Springs branch - and the staff is involved in various sorts of distance education and much focussing on vocational training, also to customers in other countries.

I conclude with a logic puzzle again. Excuse me for not giving solutions (at AI07, maybe?).

Darwin - Perth

From Darwin to Perth by bike is an incredibly long stretch of road, about 4.000 km. And the major problem is not so much the distance as such, but the distance between roadhouse. It can be up to 300 km in between two roadhouses. Good enough for 2 days of tough riding if weather conditions are not favourable. And how much water does one have to carry in such a case? If the temperature is over 35 degrees I have to drink about 10 liters a day. So for two days I'd have to carry 20 liters of water. That is unfeasible. Actually, there are people who do such things, but I prefer to depend on accidental rivers and on good samaritans under such circumstances, such as passing cars that are stopping anyway just in case you might possibly need water... In Northern Territory, water was not a problem when I travelled through because the rivers had water, I merely had to purify or boil what I took out. I was less certain about conditions in Western Australia. And indeed, once you are there, rivers dry out completely and the stretch from Port Hedland onward is devastatingly dry. I once found water there, suspiciously reddish looking: saltier than seawater. I had not much choice but still to drink it (or be really thirsty for a couple of hours, nothing more serious than that would have resulted), but I mixed it with fresh water.

But I'm skipping parts, and routing. From Katherine the first great leg was to Kununnura. Now across the part of the Northern Territory that I had seen so far the landscape is not particularly exciting: more or less flat, several meters high bushes on either side. Forever. But once you approach the Western Australian border the road passes through slightly more mountainous terrain, and the (for foreigners like me...) familiar red rock croppings, 'Ayers Rock'-like but smaller, began to appear on the horizon and on either side of the road. This is becoming very beautiful! Then, immediately after Timber Creek and just before the border, the first boab tree. Seeing a boab tree was a dream I had all my life. I used to think I had to go for Madagaskar for that. But I already knew I could expect them here too. Actually, I used to know such trees as baobab trees, but in true Aussie fashion this name was somehow abbreviated over time and, I guess, became boab. In Queensland they appear to grow too, and are known there as bottle trees. But I have never seen one there. The familiar shape of the boab tree gives the impression of a tree turned upside down: its trunk and branches are very thick, as if they were roots instead of branches. Also, in the dry period they have no leaves. Roots have no leaves either... That's why. After that first boab tree, they are omnipresent. There are amazingly beautiful hillsides with boab, yellow flowering kapok tree, and pink mulla mulla (some kind of clover-like annual). Approaching Kununnura and talking to other tourists and locals, it quickly became apparent what the main attraction was there: seeing Nicole Kidman. That gives you something to think of while on the bike. But I didn't run into her. And there was talk of some guy named Hugh Jackman, unknown to me until then, I have to confess. Surely I now want to see the movie Australia that was shot in the Kununnura area while I passed through.

It was already fairly warm weather, but after Kununnura, on my way to Broome, it became even hotter. Unbearably so. Given my experience with unsealed roads back east I had already decided to 'take the detour' by Halls Creek and Fitzroy Crossing and not 'the direct way' called the 'Gibb River Road' - though shorter, it's unsealed. But even on the regular sealed road the distances between towns outdistanced my water or at least my energy supply. It's not as if the warmer it gets the more you drink and you're fine anyway: these high temperatures also drain your energy. Also according to the locals it was 'unseasonably hot': approaching the 40s. I reached Fitzroy Crossing with very little energy left. Even 10 km before that destination I had to make another short stop to recover, drink another liter of water, and then continue (in this case battling some wind too). After arrival, first thing I went to a petrol station: airco, and two-liter bottles of milk. I drank only one, for a starter. Fitzroy Crossing is a terrible place to be, it is very clear how broken up the (large majority) Aboriginal population is in this town, and how difficult it must be to change this situation. Drunken people loitering in the streets everywhere, this is absolutely terrible to see. (My Dutch blog contains a far more detailed story on my experiences.) I befriended the local takeaway owner Terry, and we talked much on this and related topics. The combination of high temperatures and human suffering became too much for me: Terry gave me a lift out to Broome, 300 km down the road. Where I recovered in his and his partner's company, in trendy cafés on terraces and on famous Cable Beach, thus closing my eyes for the terrible situation in Fitzroy Crossing. (I have been closely following the West Australian - the quality newspaper here - on the Kimberley and on Fitzroy Crossing in particular, and it has hardly ever been out of front page coverage.)

From Broome to Port Hedland is a very desolate stretch of road, and from Port Hedland to Carnarvon as well. And the Port Hedland area is very expensive because of the booming mining activities: $160 for a motel room if you were inclined to fork that out, and $6 for a liter of milk in isolated roadhouses, well there was no way around that. The first roadhouse after Broome, 290 km down the road, burned down recently. Which I was told halfway down that road, low on supplies already (great for motivation). Fortunately it turned out, after arriving there, that the caravan park was still open, and there was water and 'some' basics. Not really the basics I'd prefer, but what can you say: coke, chocolate, pies, and hamburgers. No bread, no milk, or other basics. Fruit or vegetables you don't even expect, so let's not talk about that. Well, a bit: finally arriving in Carnarvon days and days later my first buy was a big bag of locally grown grapefruits, the most delicious I've ever tasted in my life. Somewhere halfway between Port Hedland and Carnarvon the wind turns: from always east, southeast, it changes to always west, southwest. And strong. It stayed like that more or less for the next 1500 km.

Approaching Perth you arrive in the area known for its spring flowers. I had been looking forward to that. Near Northampton (close to Geraldton) lanes of waving white torches along the road. Beautiful. Nearer to the ocean there were not that many flowers as I had expected, but more inland horizons and horizons of yellow-coloured meadows. After arriving in Perth, I've been searching catalogues all over but somehow could never find that particular flower. And there were so many of them! Mark Reynolds, my host at the University of Western Australia, helped me out of my dream: the yellow flowers are South African Daisies. And its a pest. The nice white arum lilies that flock the banks of creeks and rivers are also exotics. But they look rather nice too, I'd have to say. The waving white torches are called 'smelly socks'! Mark was a fountain of botanical and other local knowledge.

Mark Reynolds, Computer Science Department, University of Western Australia, works in temporal logics. To simplify matters, I model change with dynamic modal operators and he with temporal modal operators. His observations to my seminars there resulted in some precisions of terminology. For example, apparently I am using 'liveness' where I should be talking about 'fairness' when addressing the solution of the 'hundred prisoners and a lightbulb' riddle. Fair enough. But some other of his observations puzzled me. For example, when in another seminar I talked on arbitrary announcements and a recent exploration I am making into that area with Thomas Agotnes that relates such matters to Pauly's coalition logics, he seemed to have some objections against coalition logics of which the deep mathematical point failed to reach me. Even though the rest of the audience seemed to grasp this immediately. Then he explained it to me and I remembered his big car again with the nice poster of Mark with Kevin Rudd - it's more 'The Coalition' that his objections are about. My stay at UWA was absolutely delightful, not in the least because I also met there Tim French, one of Mark's collaborators, who had refreshing insights concerning my favourite arbitrary announcement diamond that I very much hope to explore with him further.

The logic puzzle for this leg of the trip is a classic, originally posed by Dutch topologist Hans Freudenthal in 1969, and later promoted again by John McCarthy. It is known as the 'Sum and Product'-riddle and also frequented the columns of the Mathematical Intelligencer and the Scientific American (Martin Gardner!) in the 1980s:

Perth - Melbourne

From Perth I went 'straight' to Melbourne and I did not make a stop in Adelaide. I was running out of time and I did not have any work contacts in Adelaide to visit. I made some small detours detracting me from the straightest line: there's a blob of south-eastern Australia below Perth that includes Margaret River (from the great wines - I did not taste them while there), Cape Leeuwin, and the Stirling Range of mountains. After the last couple of weeks battling against westerly winds, I had been looking forward to have them blowing from behind again. But I was thoroughly disappointed in that respect: from Albany to Adelaide I had 'mainly' easterly winds instead. They called it unseasonable, and it rained a lot too, but in fact it seems that spring weather in this part of Australia is just as changable as I am used to in New Zealand. I had a really hard time from Albany to Esperance, battling against steady and strong easterlies, which I did in the company - more or less, we were travelling the same way and then spent the night in the same camp site or hotel - of two Americans, Bob and Laurie, who were doing Perth-Sydney by bike. They impressed me because when I met them they arrived in some village pub a long time after dark in gushing down rain, having complete a 180 km stretch of road that I had 'lazily' taken two days to complete. I impressed them by travelling round in shorts and sandals in disregard of the cold and wet weather... In fact I had no choice, from Darwin I'd sent all my warm and winter outfit back home assuming not to need it ever again in the rest of the trip. How wrong I was...

The big thing down South was of course the Nullarbor Plain. I already knew that: (i) this is no desert and (ii) most of the road to follow was even forested. The actual stretch of road with 'no trees' is only 40 km wide! One reason for that is that the road is close to the coast. The railway tracks, going in parallel to the road some 100 km further north, seem to cover more actually treeless plain. The bad weather persisted more or less on this 1200 km stretch from Norseman in Western Australia to Ceduna in South Australia. It was very changeable and the wind shifted in a cycle of two or three days from a strong northerly to a strong easterly, and then southerly, and westerly, and there we go again. The thing was to know when the westerly was going to blow and then do a lot and have a rest day when the easterly was back in force. Of course this schedule did not actually work and I had to battle against winds most of the time. Another problem with these shifting winds was that northerlies came with 35+ celcius whereas southwesterlies, say, came with 20- celcius. So every other day you were back from one to the other, rather unhealthy conditions altogether so I caught a big cold and this slowed me down even further. But, finally, I made it to the other side. Is this still fun? Well, more or less. Sometimes a bit less. But you just cannot do a full circle of Australia and then give up when crossing the Nullarbor which would be the part of such a trip that everybody will later ask about first.

You know what I regret? I have seen much wildlife, but I've never seen a live emu. I would have liked to so much. Although I've seen lots of roadpizzad emus in various states of disintegration. Near Perth I saw koalas in a wildlife reserve, somewhat cheating of course as this is not in the wild. So I was agreeably surprised to see them really in the wild later: past Adelaide you have a choice between following the main road, more or less straight and flat, or doing the 'Great Ocean Road', a sizable detour again. Also, what I did not know in advance, this is a rather mountainous stretch that slows you down for sure. But, near the town of Anglesea there is a forested stretch where the koalas are all over the place. When you go past cycling you see them everywhere sitting in trees left and right of the road. This is very beautiful. At a coffeeshop next to the road you could gaze at them at leisure, they really can't be bothered a lot with all that attention as long as you don't try to cuddle such cuddly animals. They seem to have sharp claws - that can lash out if needed. Sharp claws are not surprising, as they climb up gum tree with very smooth bark.

I arrived in Melbourne on the 1st of November. Originally my host Greg Restall, Philosophy, University of Melbourne, had scheduled a seminar for me on the 2nd. But over the past weeks I had driven him mad, well at least to distraction, by tentatively reconfirming the seminar end of September, still from Perth. Then having been thoroughly battled by the weather very firmly stating from Ceduna (South Australia) that I would not make 2 November, but would probably be there in the week after that but still on time for the annual logic meeting AAL from 9 to 11 November. Then near Adelaide the weather took a turn for the better. Well, my better: a consistent storm started to blow and dump rain from the northwest. For a whole week or so. In two days I did the 400 km from Adelaide to Mount Gambier and in another two I was on the Great Ocean Road. "Oh, by the way, Greg, I'm making it to my seminar after all." "Well," he said, imperturbably friendly as ever, "by now I've scheduled someone else." But something really nice is going on here: I am now giving an 'Impromptu Melbourne Cup Logic Seminar' on Tuesday 6 November. The past weekend was incredible already. Walking through town with Stephen Cranefield and family we came across droves of girls and women in skimpy dresses and high heels and funny hats, ignoring that it's in fact cold and pouring down with rain. About half of them were walking barefeet with their $500 shoes in their hands - too much pain and discomfort I guess. Some or other racing thing was going on as well over the past weekend. As said, the coming weekend the AAL, Australasian Association for Logic, annual meeting will take place where I will meet the usual pleasant crowd before proceeding on the last stretch of my trip, back to Brisbane.

I should not forget to mention the incredible Trinity College where I am staying, on the Melbourne University campus. And mention it honourably! It's always a bit of a guess where you end up while staying in a town and a more welcome reception than that given by Sally Dalton-Brown and her staff and colleagues is unimaginable. I am writing this blog behind the computer in my Trinity College room, surrounded by reproductions of 14th-15th centuries paintings and with the Encyclopedia of the British Empire at hand in case I were to need it. Looking out on the sports oval of the campus. Dining takes place in a grand dining area with all massive wooden tables and chairs and an equally massive wooden ceiling, in true Oxbridge style. If you read this, are an academic, and ever spend time visiting Melbourne University: stay at Trinity!

The following riddle originally came to me by way of Marc Pauly, by way of Valentin Shehtman, by way of Alexander Shen. It was posed at the 2000 Moscow Mathematics Olympiad. I recently discovered that its origin is much older: it also figures as a motivating example in the combinatorics classic: W.D. Wallis, Combinatorial Designs, 1988 (M. Dekker, New York). (Page 1 to 3 explores it.)

Melbourne - Brisbane

I had to draw myself away from Melbourne University and the wonderful accommodation in Trinity College. But I finally did, halfway the second day of AAL 2007, unkindly interrupting Bob Meyer's presentation when waiving everyone goodbye on my bike. I couldn't resist a slight detour towards Sydney, by way of Gippsland, thus avoiding the major road. This proved to be a good idea. Gippsland is rather 'New-Zealand-like' (this must sound like an insult to Australians, but it is intended as a compliment) with green pastures, lots of cattle and sheep, and lots of waterways all around. Gippsland had just been drenched the week before, and some roads had only recently been reopened after flooding. (Doesn't that sound tyically New-Zealandish...) After Bairnsdale, still on the coast, I was planning to go somewhat inland, and go to Sydney by way of Canberra - you can't really make a tour of Australian universities but miss out on ANU. I intended to follow a fairly major road but fortunately I ran into an American cyclist who persuaded me to join him doing a high mountain pass over the Australian Alps, towards Jindabyne. This turned out to be an exceedingly good idea, because apart from pleasant company this meant very quiet roads. The route more or less follows the Snowy River, the actual pass is 1350 meters, just before Jindabyne.

At ANU I was hosted by Rajeev Goré, we inevitably discussed tableaux for dynamic epistemic logics, and I had also found out that Joe Salerno, expert on matters concerning Fitch knowability, accidentally happened to be on sabbatical in Canberra. So this was all very nice and productive. I should not forget to mention that Diane Kossatz kindly gave me a ANU Logic Summerschool 2007 T-shirt even before the event took place! Visits to RSISE in Canberra are incomplete unless you are showered by her unlimited kindness. At my ANU seminar I was quite surprised to see two familiar faces enter the room, namely Chris Monteith and Tim Jones, both formerly from Otago and now PhD students at ANU.

Di Kossatz also told me about available accommodation in Sutton, some 20 km from Canberra. I departed rather late on the Tuesday and wanted a lazy start. Circling through and around Sutton I did not find this place after all, so continued towards Goulburn on the so-called Federal Highway. As Di had also told me that the next township, Collector, unlike Sutton did not have accommodation, I stopped along the shores of (completely empty) Lake George just before dark, and set up my tent just over a high bank along the Federal Highway. Bugger! I had been hoping for more luxury this night! The next day, when passing Collector within the hour, it turned out that there was a hotel with accommodation after all in that town...

Given some alternative roads through the area it was not very smart to keep following the - by now called - Hume Highway (four lanes, though fairly quiet). But I had cornered myself by accepting an invitation from Yan Zhang, University of Western Sydney, to give a seminar next day's afternoon. That meant cycling on at high speed towards Penrith! So I did... Reaching Mittagong, you come quite close to where the metropolitan area of Sydney starts. Close enough. Made it! A mere 100+ km to go, before the obligation to reach Penrith next day noon sharp. Another bad accommodation decision made me then go on towards Penrith hoping to find a room along the way, towards the evening. This route follows the railway tracks, more or less, of the Sydney-Canberra line (or of some parallel tracks, I am not quite sure) somewhat to the North/West of the Hume Highway, along fairly quiet roads and beautiful scenery. Dense forests again, on the seaside of the continental divide. The accommodation did not come forward. One small town after the other... (Hilltop, Balmoral, Buxton, Thirlmere, ...) The hours passed, I already was fairly tired and now I was really very tired. At a road corner on my way from Thirlmere towards Penrith I saw a sign 'Mowbray Park farmstays'. I followed the sign, passed lots of whitewashed gates and fences, and arrived at an impressive complex of end-of-19th-century buildings with a mansion and stables, and lots, lots of horses. No humans. It took some 15 minutes before I found someone on this large outfit and indeed finally found my soft bed and good sleep for the night. Because of the horse fever, activities on Mowbray Park had slowed down to next to nothing, a huge loss of business opportunity for these people.

From Yan Zhang's group at the University of Western Sydney (we discussed interesting work on the logic of forgetting, and I was quite please to formulate several new solutions together with Volker Gebhardt to the '100 prisoners and a lightbulb' riddle, while he had to wait an hour for a pickup) I moved on quickly to Ron van der Meyden, at NICTA. There I met many others of my acquaintance, Norman Foo busy campaigning for the Greens (the elections where the next day), Rob van Glabbeek who had just moved to a new house, ... Ron put me up in the Coogee Beach Crowne Plaze which is probably the most luxury hotel I ever stayed at. (At some stage it is unclear to me how meaningful 'more luxury' is. Yes, I could choose between five different bars of handsoap. Between two king-size beds. Three sorts of shampoo. Do I want that? Not really. Should I want that?) It was so high-class that the management did not even turn an eyebrow, blink, or be otherwise flabbergasted, by a cyclist in full gear turning up at the lobby. "Would you like us to park your vehicle in the basement?" In the end, I could simply keep it in my room - newspapers under it to protect the thick luxury carpet. With Ron I share an interest in information-based security and he is also involved in a Lorentz workshop in Leiden, next year, that I am organizing.

This part of the trip is more and more talk about universities and academics and less and less about Australian scenery and bicycles. Apologies! Back to cycling again. From Sydney to Brisbane was probably the most dangerous part of the whole trip. The Pacific Highway is the major road between those metropolis, and, guess what, it's a single-lane-each-way road for most of that way. This is horrible on a bicycle. Also many bridges on that road are quite old and therefore even narrower than the road itself, that might already have shouldered out in the mean time. Just get on the bridge, keep moving, and try to ignore trucks. Unfortunately they behave the same towards me. (Also, if you allow me, overall an 'unfriendly australian' is somewhat of a contradiction in terms; but in New South Wales you definitely meet that kind much more often than in any other part of Australia I have seen, and not even just on the road.) I heard the new Australian government intends to spend 2.5 billion AU$ on improving that road. That will be well spent.

The very beforelast day of the cycling part of my trip I spent on a camping ground at the base of Mount Warning, very close to Gold Coast. Near Brisbane the vegetation becomes more and more tropical again, sugar cane, pineapples, and bananas. The mountains are very beautifully and weirdly shaped here. Strange contraptions rising out of the plain. Seen from a large distance, covered from base to top with a green carpet without bare rocky patches, no matter how steep or even overhanging. And the very last day there remained only some 50 km to my pickup point in Gold Coast: Guido Governatori picked me up again, just as he had dropped me north of Brisbane at the beginning of the trip - the most remarkably host you'd ever encounter. As meeting point he had asked me to wait at the Pizzahut Restaurant on Kirra Beach, Coolangatta. So I was forced to eat Pizzahut pizza, there directed by an Italian of all people. Never mind.

Apart from the last day cycling, there was of course the very very actual last day of the trip: the 'logic puzzle and other fun' presentation at the Australian AI 07 conference. Given my impossible flight schedule this had been deferred from the congress banquet to the congress reception, but Guido's impeccable organization made this a success, yet again. Surrounded by congress participants I solved the '100 prisoners and a lightbulb riddle' including some of its versions, with one slide and a lot of words, interspersed with pictures from the trip (see also below!). Of course, how could that fail, I ran into yet another former Otago (graduate) student, at AI 07: Yun Sing Koh, currently at Auckland University of Technology. Next year's Australian AI will be organized at AUT, rebaptized to Australasian AI conference. After my last words at AI07, early the next morning, I hastened to Brisbane Airport with my bike - or rather: Guido hastened me. The final surprise of the trip was luggage handling calling me before departure of the plane. They were worried about the red bikelight continuously turning on and off. It's some Dutch-made device, sensitive to light and motion: if dark and moving, on; otherwise, off. After discussing various options (remove battery?) they were satisfied by the low voltage of such lights, and let it and me on the plane.

The final riddle (apparently by way of Yoav Shoham) is one that I received from Dongmo Zhang, University of Western Sydney, after my presentation there. I slightly adapted the formulation, trying to remain faithful to the original. For 'the right answer' you should read 'the pair M/N', and Alice's first announcement could equivalently have read "Alice: Bob does not know the answer," or "Alice: Both I and Bob do not know the answer."

Dongmo also suggested that epistemic puzzles like those presented in this weblog might have been around in China already for a long time. That would be very interesting. So far, to my knowledge, there are none from before the 1940s. Such entertainment is often not considered as a serious academic pursuit - even though it motivates the development of new ideas and new theory. Therefore, people mostly do not bother to give a source for their riddle, which therefore finally gets lots in the fog of academic history. Anyone who knows anything about the origin of logic puzzles: please contact me!