您在正确的轨道上！继续前进，您将获得如下信息：
expr(Xs0,Xs) :- % expr --> term(Xs0,Xs1), % term, addterm(Xs1,Xs). % addterm.addterm(Xs0,Xs) :-% addterm --> Xs0 = Xs. % [].addterm(Xs0,Xs) :-% addterm --> Xs0 = [+|Xs1], % [+], expr(Xs1,Xs). % expr.term(Xs0,Xs) :- % term --> factor(Xs0,Xs1), % factor, multfactor(Xs1,Xs). % multfactor.multfactor(Xs0,Xs) :- % multfactor --> Xs0 = Xs. % [].multfactor(Xs0,Xs) :- % multfactor --> Xs0 = [*|Xs1], % [*], term(Xs1,Xs). % term.factor(Xs0,Xs) :- % factor --> Xs0 = [I|Xs], % [I], integer(I). % {integer(I)}.factor(Xs0,Xs) :- % factor --> Xs0 = ['('|Xs1], % ['('], expr(Xs1,Xs2), % expr, Xs2 = [')'|Xs]. ` % [')'].
