Program remember answer
Source: Building Expert Systems in PROLOG Publisher
Program source code: answers_storing.pl
ask(A, V):- known(yes, A, V), % succeed if true !. % stop looking ask(A, V):- known(_, A, V), % fail if false !, fail. ask(A, V):- write(A:V), % ask user write('? : '), read(Y), % get the answer asserta(known(Y, A, V)), % remember it Y == yes. % succeed or fail