s
step:
goal:
grandparent(1$_$_2?Z,1$_$_2?X)./2
goallist:
grandparent(1$_$_2?Z,1$_$_2?X)./2
gender(1$_$_2?Z,female)./2
substitution:
[(_1?Z,1$_$_2?Z)(_1?X,1$_$_2?X)]
history:
(grandparent(1$_$_2?Z,1$_$_2?X),gender(1$_$_2?Z,female)
:> grandmother(1$_$_2?Z,1$_$_2?X)./2,grandmother(_1?Z,_1?X)./10)