#!/usr/bin/prolog

%if(and(young,poor),student)

:- op(999,xfx,if).
:- op(998,xfy,or).
:- op(997,xfy,and).
:- op(997,fy,not).

student if
 young and poor and not dumb.

dumb if not smart.

cf(young,0.4).
cf(poor,0.9).
cf(smart,0.9).

belief(X,Y) :- cf(X,Y).
belief(X,Cf) :-
	X if Z,
	belief(Z,Cf).

belief(X and Y,CF0) :-
	belief(X,CF1),
	belief(Y,CF2),
	CF0 is min(CF1,CF2).

belief(X or Y,CF0) :-
	belief(X,CF1),
	belief(Y,CF2),
	CF0 is max(CF1,CF2).

belief(not X,CF0) :-
	belief(X,CF1),
	CF0 is 1 - CF1.