/*infer*/
/*LOGO type inference package
Alan Bundy 16.11.79*/


/*infer fact by backwards inference*/
infer(Goal) :- infer(Goal,now).

infer(Goal,Sit) :- fact(Goal,Sit).

infer(Goal,Sit) :-
        backward_rule(Ant,Goal), infer(Ant,Sit).

infer(Goal1&Goal2,Sit) :-
        infer(Goal1,Sit), infer(Goal2,Sit).

/*assert fact and trigger forwards inference*/
assert_fact(Fact) :- assert_fact(Fact,now).

assert_fact(Fact,Sit) :-
        assert(fact(Fact,Sit)),
        writef('asserting %t in situation %t\n',[Fact,Sit]),
        forall(forward_rule(Fact,New),assert_fact(New,Sit)).