Pullback-stable regular epimorphisms - #344
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Paused since I am on vacation
This PR adds the last remaining constitutent property of regular categories (cf. #343): having pullback-stable regular epimorphisms. For convenience, it is required that pullbacks exist. The dual property, having pushout-stable regular monomorphisms, is added as well.
TODO. Try to decide the 6 remaining unknown cases.
Decide pullback-stable regular epis for
For Unif we equivalently need to decide if it is regular (probably not); for the other two it is already known that they are not.
Decide pushout-stable regular monos for
For every one of these we equivalently need to decide if it is coregular. See also #317 which contains a sketch that Unif is coregular.