% An example based on p262 of Appleby 91 'Programming Lnguages'
% This uses a simplified english grammar.
:-consult('/u/faculty/dick/cs320/prolog/english.pl').
:-verb([watches]).
:-pred([is_happy]).

X is_happy:-X watches football, X has supplies.
X has supplies:-X has beer, X has pretzels.
X watches football:-X sees T, T isa tv, X owns T, T is_on.
T is_on:-cowboys on T. 
tom owns his_tv. his_tv isa tv.
tom sees his_tv.
cowboys on his_tv.
tom has beer.
tom has pretzels.
dick has beer. dick owns two_tvs. two_tvs isa tv.
harry has pretzels.
joan has beer. joan has pretzels. joan has her_radio. her_radio is_on.

:- write('Monday night is now'), nl.
:-print('Words defined: is_happy, is_on, has, supplies, beer, pretzels, tom...').
:- write('Try:  Who is_happy? and listing!'), nl.
why:-pp postfix is_happy; pp infix has; pp infix owns; pp infix isa.
why:-pp infix sees; pp postfix is_on.