frequents(achim, herkules).
frequents(karin, herkules).
frequents(achim, bockshaut).
frequents(joseph, bockshaut).
frequents(lena, bockshaut).
serves(herkules, becks).
serves(bockshaut, grohe).
serves(bockshaut, paulaner).
likes(karin,grohe).
likes(achim,grohe).
likes(joseph,grohe).


happy(D)              :- frequents(D,P), serves(P, B),
                         likes(D,B).

should_visit(D,P)     :- serves(P,B), likes(D,B).

not_should_visit(D,B) :- frequents(D,_), serves(B,_), not( should_visit(D,B) ).

not_very_happy(D)     :- frequents(D,P), not_should_visit(D,P) .

very_happy(D)         :- frequents(D,_), not( not_very_happy(D) ).

sad(D)                :- frequents(D,_), not( happy(D) ).