(1) The direct product <수식> E_i of BCK-algebras E_i, (i=1,2,3,…,n), is a BCK-algebra. (2) Let E be a BCK-algebra and A₁, A₁,…, A_n ideals of E. Define a mapping <수식> by the rule f(x)=(A₁x, A₂x, …, A_nx) . Then f is a homomorphism.
