Rules and Disjunctions

Someone is happy if they are healthy, wealthy or wise.

 
happy(Person):-

		       healthy(Person).

happy(Person):-

		       wealthy(Person).

happy(Person):-

		       wise(Person).

Note how we have had to rewrite the original informal statement into something like:

Someone is happy if they are healthy OR
Someone is happy if they are wealthy OR
Someone is happy if they are wise

We have also assumed that each clause is (implicitly) universally quantified. i.e. the first one above represents X.(healthy(X)happy(X)).

The predicate name ``happy' is known as a functor. (Any predicate name is a functor).

The functor happy has one argument.

We describe a predicate with name ``predname'' with arity ``n'' as predname/n. It has one argument ---we say its arity is 1.

The predicate happy/1 is defined by three clauses.