@prefix : .
@prefix family: .
:Person(family:peter).
:Person(family:tom).
family:hasParent(family:tom,family:peter).
family:hasChild(family:tom,family:peter).
family:hasParent(B,A) :- family:hasChild(A,B).
:- family:hasParent(A,B), family:hasParent(B,A).