From fe48a462f51be174e492e5b1af9bbfc80235e355 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ya=C3=ABl=20Dillies?= Date: Fri, 11 Oct 2024 07:51:10 +0000 Subject: [PATCH] feat: `SpecialLinearGroup n R` is finite when `R` is (#17629) From GrowthInGroups --- Mathlib/LinearAlgebra/Matrix/SpecialLinearGroup.lean | 3 +++ 1 file changed, 3 insertions(+) diff --git a/Mathlib/LinearAlgebra/Matrix/SpecialLinearGroup.lean b/Mathlib/LinearAlgebra/Matrix/SpecialLinearGroup.lean index abb3fa721cfad..261b976d62a38 100644 --- a/Mathlib/LinearAlgebra/Matrix/SpecialLinearGroup.lean +++ b/Mathlib/LinearAlgebra/Matrix/SpecialLinearGroup.lean @@ -124,6 +124,9 @@ instance : Pow (SpecialLinearGroup n R) ℕ where instance : Inhabited (SpecialLinearGroup n R) := ⟨1⟩ +instance [Fintype R] [DecidableEq R] : Fintype (SpecialLinearGroup n R) := Subtype.fintype _ +instance [Finite R] : Finite (SpecialLinearGroup n R) := Subtype.finite + /-- The transpose of a matrix in `SL(n, R)` -/ def transpose (A : SpecialLinearGroup n R) : SpecialLinearGroup n R := ⟨A.1.transpose, A.1.det_transpose ▸ A.2⟩