son and parents

son and parents
PREDICATES
husband(STRING,STRING)
father(STRING,STRING)
mother(STRING,STRING)
son(STRING,STRING)
CLAUSES
mother("Kushalya","Ram").
mother("Kaikai","Bharat").
mother("Sumitra","Laxman").
mother("Sumitra","Satrughan").
husband("Dasrath","Kaushalya").
husband("Dasrath","Kaikai").
husband("Dasrath","Sumitra").
son(A,C):- mother(C,A).
son(A,C):-husband(C,B), mother(B,A).
father(A,B):- husband(A,C), mother(C,B).
GOAL
son(X, "Kaikai").