English
The complement of a prime ideal P is a submonoid of the ambient ring; it contains 1 and is closed under multiplication.
Русский
Комплемент простого идеала P образует подмономоид кольца; он содержит 1 и замкнут по умножению.
LaTeX
$$P^{\mathrm{c}} \text{ is a submonoid of } \alpha, \ 1 \in P^{\mathrm{c}}, \ \forall x,y \in P^{\mathrm{c}},\ xy \in P^{\mathrm{c}}$$
Lean4
/-- The complement of a prime ideal `P ⊆ R` is a submonoid of `R`. -/
def primeCompl (P : Ideal α) [hp : P.IsPrime] : Submonoid α
where
carrier := (Pᶜ : Set α)
one_mem' := P.one_notMem
mul_mem' {_ _} hnx hny hxy := Or.casesOn (hp.mem_or_mem hxy) hnx hny