dininghallhas(M) :- icecream(M).
icecream(vanilla).

sibling(X,Y) :- parent(Z,X), parent(Z,Y).
mother(X,Y) :- parent(X,Y), female(X).
uncle(X,Y) :- parent(Z, Y), sibling(Z,X), male(X).
female(lady). female(dne). male(jack).
parent(lady, jack). parent(lady,dne ).