English
There is a topological group isomorphism between P and the limit of its quotients, provided by continuousMulEquivLimittoFiniteQuotientFunctor.
Русский
Существует топологический изоморфизм между P и пределом ее фактор-групп, задаваемый continuousMulEquivLimittoFiniteQuotientFunctor.
LaTeX
$$$P \cong_{t*} \mathrm{limit}(P.toFiniteQuotientFunctor \cdot \mathrm{forget}_{\mathrm{FiniteGrp}\to \mathrm{ProfiniteGrp}})$$$
Lean4
/-- The topological group isomorphism between a profinite group and the projective limit of
its quotients by open normal subgroups -/
noncomputable def continuousMulEquivLimittoFiniteQuotientFunctor (P : ProfiniteGrp.{u}) :
P ≃ₜ* (limit (toFiniteQuotientFunctor P ⋙ forget₂ FiniteGrp ProfiniteGrp)) :=
{
(Continuous.homeoOfEquivCompactToT2 (f := Equiv.ofBijective _ ⟨toLimit_injective P, toLimit_surjective P⟩)
P.toLimit.hom.continuous_toFun) with
map_mul' := (toLimit P).hom.map_mul' }