bimodule
Let R and S be rings. An (R,S)-bimodule isan abelian group M which is a left module over R and a rightmodule over S such that the r(ms)=(rm)s holdsfor each r in R, m in M, and s in S.Equivalently, M is an (R,S)-bimodule if it is a leftmodule over or a right module over.
When M is an (R,S)-bimodule, we sometimes indicate thisby writing the module as .
If P is a subgroup of M which is also an(R,S)-bimodule, then P is an(R,S)-subbimodule of M.