# Epimorphisms in varieties of subidempotent residuated structures

## TL;DR

This paper proves that epimorphisms are surjective in certain varieties of subidempotent residuated structures, extending previous results to broader classes including De Morgan monoids.

## Contribution

It establishes conditions under which epimorphisms are surjective in varieties of subidempotent residuated lattices, generalizing earlier findings to new algebraic structures.

## Key findings

- Epimorphisms are surjective in the specified varieties.
- Conditions on finitely subdirectly irreducible algebras are necessary.
- The results extend to varieties with bounds and include De Morgan monoids.

## Abstract

A commutative residuated lattice A is said to be subidempotent if the lower bounds of its neutral element e are idempotent (in which case they naturally constitute a Brouwerian algebra A*). It is proved here that epimorphisms are surjective in a variety K of such algebras A (with or without involution), provided that each finitely subdirectly irreducible algebra B in K has two properties: (1) B is generated by lower bounds of e, and (2) the poset of prime filters of B* has finite depth. Neither (1) nor (2) may be dropped. The proof adapts to the presence of bounds. The result generalizes some recent findings of G. Bezhanishvili and the first two authors concerning epimorphisms in varieties of Brouwerian algebras, Heyting algebras and Sugihara monoids, but its scope also encompasses a range of interesting varieties of De Morgan monoids.