from agents import *
from logic import *
A, B, C, D, E, F, G, P, Q, x, y, z, F, G, u = map(Expr, 'ABCDEFGPQxyzFGu')
unify(P(A, x, F(G(y))), P(z, F(z), F(u)))
{z: A, x: F(z), u: G(y)}
=> I think this should return instead {z: A, x: F(A), u: G(y)}

The unifier returned does not make the two expressions identical as it should

subst({z: A, x: F(z), u: G(y)}, P(A, x, F(G(y))))
P(A, F(z), F(G(y)))
subst({z: A, x: F(z), u: G(y)}, P(z, F(z), F(u)))
P(A, F(A), F(G(y)))