mathlib3

1f1289fc - feat(algebra/parity + data/{int, nat}/parity): parity lemmas for general semirings (#12718)

feat(algebra/parity + data/{int, nat}/parity): parity lemmas for general semirings (#12718) This PR proves some general facts about adding even/odd elements in a semiring, thus removing the need to proving the same results for `nat` and `int`.