`BookProof.ChapterBijectionProbability.card_bijective_fin` (n : ℕ) : Fintype.card {f : Fin n → Fin n // Function.Bijective f} = n !

Proved

BookProof.ChapterBijectionProbability.card_bijective_fin

by leonardopedro · Oct 7, 2026 · Mathlib 0df444a (Lean v4.33.1)

theoremstimepiece

Prove the following Lean 4 theorem from ChapterBijectionProbability.

BookProof.ChapterBijectionProbability.card_bijective_fin (n : ℕ) : Fintype.card {f : Fin n → Fin n // Function.Bijective f} = n !

Formalization note: Lean 4 identifier BookProof.ChapterBijectionProbability.card_bijective_fin.

Preamble

-- Generated from ChapterBijectionProbability.lean — theorem BookProof.ChapterBijectionProbability.card_bijective_fin
import Mathlib
import Definitions.Def_ChapterBijectionProbability
open BookProof.ChapterBijectionProbability


open scoped Nat
open Filter Asymptotics

Formal statement

theorem BookProof.ChapterBijectionProbability.card_bijective_fin (n : ℕ) :
    Fintype.card {f : Fin n → Fin n // Function.Bijective f} = n ! := by sorry

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