二つのベクトル空間("v",+,{αk}"k"∈"k"),("w",+′,{β"k"}"k"∈"k")(βk: "w" → "w"; β"k"("w"):＝ "kw" for "k" ∈ "w")の間の準同型 "f": "v" → "w" は