% An example based on p262 of Appleby 91 'Programming Lnguages'
happy(X):-watching(X, football), has(X,supplies).
has(X, supplies):-has(X,beer), has(X, pretzels).
watching(X, football):-ison(X, tv), playing(cowboys).
ison(tom, tv).
playing(cowboys).
has(tom,beer).
has(tom,pretzels).
has(dick,beer).
has(harry,pretzels).
ison(dick,tv).
ison(joan,radio).
has(joan,pretzels).
has(joan,beer).

:- write('happy(Person) is loaded'), nl.
:- write('try queries like:  happy(X).  has(X,beer).  has(tom, X). '),nl,nl.