ti(G_0, (A_0,B_0,C_0)) :-
   G_0 = (C_0,A_0,B_0),
   C_0 = unify_with_occurs_check(_,_),
   skel(A_0),
   skel(B_0),
   f(G_0).

f((unify_with_occurs_check(A,B),unify_with_occurs_check(A,[]*C),unify_with_occurs_check(C,B*_D))).

skel(unify_with_occurs_check(_,_*_)).