vorspeisen_available([wurstsalat, zwiebelsuppe]). meat_available([rinderbraten, brathahnchen, schweinekotelett]). fish_available([matjesfilet, blaue_forelle]). nachspeisen_available([apfelstrudel, obstsalat]). meal(H, M, D) :- hors_d_oeuvre(H), maincourse(M), dessert(D). maincourse(M) :- meat(M). maincourse(M) :- fish(M). member(X, [X|Xs]). member(X, [Y|Ys]) :- member(X, Ys).