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Every finite nilpotent loop has a supernilpotent loop as reduct

Group Theory 2025-12-03 v3

Abstract

A basic fact taught in undergraduate algebra courses is that every finite nilpotent group is a direct product of pp-groups. Already Bruck observed that this does not generalize to loops. In particular, there exist nilpotent loops of size 66 which are not direct products of loops of size 22 and 33. Still we show that every finite nilpotent loop (A,)(A,\cdot) has a binary term operation * such that (A,)(A,*) is a direct product of nilpotent loops of prime power order, i.e., (A,)(A,*) is supernilpotent. As an application we obtain that every nilpotent loop of order pqpq for primes p,qp,q has a finite basis for its equational theory.

Keywords

Cite

@article{arxiv.2409.12484,
  title  = {Every finite nilpotent loop has a supernilpotent loop as reduct},
  author = {Michael Kompatscher and Peter Mayr},
  journal= {arXiv preprint arXiv:2409.12484},
  year   = {2025}
}
R2 v1 2026-06-28T18:49:50.003Z