have A : ∀ (k) (σ : fiber α k), card (fixedPoints (↑σ : Perm α)) = k := fun k σ => σ.2
α : Type u_1
inst✝¹ : Fintype α
inst✝ : DecidableEq α
⊢ ∑ k ∈ range (card α + 1), k * p α k = card α * (card α - 1)!
α : Type u_1
inst✝¹ : Fintype α
inst✝ : DecidableEq α
A : ∀ (k : ℕ) (σ : ↑(fiber α k)), card ↑(fixedPoints ⇑↑σ) = k
⊢ ∑ k ∈ range (card α + 1), k * p α k = card α * (card α - 1)!