Definition 1. An algebra (X; ∗, 1) of type (2, 0) is called a BE-algebra if
(BE1) x ∗ x = 1 for all x ∈ X;
(BE2) x ∗ 1 = 1 for all x ∈ X;
(BE3) 1 ∗ x = x for all x ∈ X;
(BE4) x ∗ (y ∗ z) = y ∗ (x ∗ z) for all x, y, z ∈ X (exchange)
We introduce a relation “≤” on X by x ≤ y if and only if x ∗ y = 1.