On the characterization of Jónsson-Tarski and of subtractive varieties
arXiv:1404.5477
Abstract
We investigate unital, subtractive and strongly unital regular categories with enough projectives and give characterizations of their projective covers. The categorical equation "strongly unital = unital + subtractive" is explored: this leads to proofs of their varietal characterizations in terms of the categorical properties of the corresponding algebraic theories.
12 pages