Proposition 3.10. If X is a self distributive BE-algebra, then it is transitive.
Proof. For any x, y ∈ X, we have
(y ∗ z) ∗ [(x ∗ y) ∗ (x ∗ z)] = (y ∗ z) ∗ [x ∗ (y ∗ z)] [self distributive]
= x ∗ [(y ∗ z) ∗ (y ∗ z)] [(BE4)]
= x ∗ 1 [(BE1)]
= 1 [(BE2)],
proving the proposition.