ABSTRACT
A ring A is said to be H-separable over a subring B if A ®B A is isomorphic to a direct summand of n copies of A as (A-A)-bimodules for some positive n. It follows that A, the centralizer of B in A, is a finitely generated projective C-module, where C is the center of A; and also that A⊗ BA is isomorphic to Hom c (Δ, A) as (A-A)-bimodules. In fact, these last two conditions together are equivalent to A being H-separable over B.
