We introduce a relation “≤” on X by x ≤ y imply x ∗ y = 1. An CI-algebra
(X, ∗, 1) is said to be self-distributive if x ∗ (y ∗ z) = (x ∗ y) ∗ (x ∗ z) for all
x, y, z ∈ X. A non-empty subset S of an CI-algebra X is said to be a subalgebra
of X if x ∗ y ∈ S whenever x, y ∈ S.