Family domain experiment 3: results.
MPL
1. father(X,Y) :- parent(X,Y).
2. grandfather(X,Y) :- male(X), parent(X,Z), parent(Z,Y).
ATRE
1. father(X1,X2) :- parent(X1,X2).
2. grandfather(X1,X2) :- father(X3,X2) =. true,father(X1,X3) =. true,male(X1) =. true.