Prolog Logic Statements

chocolate(P) :- place(P).
vanilla(P) :- not(place(P)).
place(dininghall).

cousin(X, B) :- parent(Z, X), sibling(Z, A), parent(A,B).
parent(usha, veena). parent(bapu, ash).
sibling(usha, bapu).

%query-cousin(veena, ash).   console- yes
%query-chocolate(dininghall). console- yes
%query-vanilla(dininghall).  console- no