Hi, i have a problem with this prolog:
sister(X,Y):- woman(X), father(Z,X), father(Z,Y), X\=Y.
sister(X,Y):- woman(X), mother(Z,X), mother(Z,Y), X\=Y.
woman(carla).
woman(maria).
woman(anna).
mother(carla, giovanni).
mother(carla, anna).
mother(carla, maria).
father(luigi, maria).
father(pasquale, maria).
If i use prolog's interpreter and i submit this query: "sister(maria, X)", Prolog gives me one solution (X=giovanni) if i type two time enter, and it gives me all solution if i types enter one time following by differents space for the each other solution. But at the end for the second case, it gives me "false". Why doesn't Prolog give me all solution when i run query the first time?
Thanks.