Abstract
Let (A(0), A(1)) be a compatible couple of normed spaces. We study the interrelation of the general K-interpolation spaces of the couple (A(0) + A(1), A(0) boolean AND A(1)) with those of the couples (A(0), A(1)), (A(0) + A(1), A(0)), (A(0) + A(1), A(1)), (A(0), A(0) boolean AND A(1)), and (A(1), A(0) boolean AND A(1)).