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

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`BookProof.ChapterBijectionProbability.card_bijective_fin` (n : ℕ) : Fintype.card {f : Fin n → Fin n // Function.Bijective f} = n ! · Prove2Me