Commutative-monoid enrichment (source code)

= Commutative-monoid enrichment

= Semi-additive structure
{synonym}

A commutative-monoid enrichment gives each hom-set a <commutative monoid> structure, with zero and addition, so that composition distributes over addition in both variables and annihilates zero. This is called a semi-additive structure in some conventions, including Cambridge Part III paper 119 of 2017. Other conventions reserve <semi-additive category> for categories with this enrichment and finite <biproducts>. A one-object category arising from a <semiring> has the enrichment without generally having those finite products.