Lemma that, in an Abelian category, a short exact sequence, one of whose two morphisms admits a section or retraction into the middle term, is a direct sum
la lemo ke, en Abel-a kategorio, mallonga ekzakta vico, unu el kies du morfioj havas unuflankan inverson en la mezan termon, estas rekta sumo (eo)
lemma that, in an Abelian category, a short exact sequence, one of whose two morphisms admits a section or retraction into the middle term, is a direct sum (en)