Cover Relations on Categories

A cover relation on a category ℂ is a binary relation ⊏ on the class of morphisms of ℂ, which is defined only for those pairs of morphisms which have the same codomain, and which has the following two properties: (i) if f ⊏ g and h is composable with f, then hf ⊏ hg, (ii) if f ⊏ g and f is composable with e then fe ⊏ g. We study cover relations arising from a special type of factorization systems, and cover relations arising from a special type of monoidal structures. Supported by Claude Leon Foundation, INTAS (06-1000017-8609) and Georgian National Science Foundation (GNSF/ST06/3-004).