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PreprintCC BY 4.0arXiv

The strong nonfinite basis property of S7

Abstract

We prove that the three-element additively idempotent semiring S7 is strongly nonfinitely based: every finite additively idempotent semiring whose generated variety contains S7 has no finite equational basis. This answers Problem~1.2 in Yue, Ren and Gao's paper Explicit equational bases for the power semirings of S7 affirmatively. The proof combines a rigidity property of set systems with private points and a probabilistic construction derived from semilinear sets of letter counts in finite semigroups. The argument allows arbitrary polynomial substitutions and does not assume commutative multiplication. As consequences, both power semirings of the multiplicative reduct of S7, and both power semirings of every finite group of order at least three, are strongly nonfinitely based. All algebras are considered in the signature (+,·) without nullary operations.

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BibTeX
@misc{wang2026strong,
  title = {{The strong nonfinite basis property of $S_7$}},
  author = {Lili Wang and Qingrui Yin and Aifa Wang},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.13980},
  eprint = {2610.13980},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.13980},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - The strong nonfinite basis property of S_7
AU  - Lili Wang
AU  - Qingrui Yin
AU  - Aifa Wang
PY  - 2026
DA  - 2026/10/01
PB  - arXiv
DO  - 10.48550/arxiv.2610.13980
UR  - https://arxiv.org/abs/2610.13980
AB  - We prove that the three-element additively idempotent semiring S_7 is strongly nonfinitely based: every finite additively idempotent semiring whose generated variety contains S_7 has no finite equational basis. This answers Problem~1.2 in Yue, Ren and Gao's paper Explicit equational bases for the power semirings of S_7 affirmatively. The proof combines a rigidity property of set systems with private points and a probabilistic construction derived from semilinear sets of letter counts in finite semigroups. The argument allows arbitrary polynomial substitutions and does not assume commutative multiplication. As consequences, both power semirings of the multiplicative reduct of S_7, and both power semirings of every finite group of order at least three, are strongly nonfinitely based. All algebras are considered in the signature (+,·) without nullary operations.
ER  -