1.2 PROLOG的程序
PROLOG程序一般由一组事实、 规则和问题组成。
问题是程序执行的起点, 称为程序的目标。
likes(bell,sports).
likes(mary,music).
likes(mary,sports).
likes(jane,smith).
friend(john,X):-
likes(X,reading),likes(X,music).
friend(john,X):-likes(X,sports),likes(X,music).
?-friend(john,Y).