We have converted the Simpsons-Bouvier family tree into prolog relations. Now we will use these to define more complicated relations.

Implement following relations:

• is_mother(X): X is a mother
• is_father(X): X is a father
• is_son(X): X is a son
• sister_of(X,Y): X is a sister of Y
• grandpa_of(X,Y): X is a grandfather Y
• sibling(X,Y): X is a sibling of Y

You may use the relations father(Father,Child) and mother(Mother,Child), male(X) and female(X).