For abelian groups G and H which are written additively, the direct product of G and H is also called a direct sum (Mac Lane & Birkhoff 1999, §V.6).
加法的に書かれるアーベル群 G と H に対して、G と H の直積 (direct product) はまた直和 (direct sum) とも呼ばれる (Mac Lane & Birkhoff 1999, §V.6)。