rw [move_p hvi hj hk]
α : Type u_1
inst✝¹ : Fintype α
inst✝ : DecidableEq α
i : ℕ
v : α
j k : ℕ
M : MultiPart α
hvi : i ∈ range (M.t + 1) ∧ v ∈ MultiPart.P M i
hj : j ∈ range (M.t + 1) ∧ j ≠ i
hk : k ∈ range (M.t + 1)
⊢ card ((move M hvi hj).A \ MultiPart.P (move M hvi hj) k) =
    if k ≠ i ∧ k ≠ j then card (M.A \ MultiPart.P M k)
    else if k = i then card (M.A \ MultiPart.P M i) + 1 else card (M.A \ MultiPart.P M j) - 1
α : Type u_1
inst✝¹ : Fintype α
inst✝ : DecidableEq α
i : ℕ
v : α
j k : ℕ
M : MultiPart α
hvi : i ∈ range (M.t + 1) ∧ v ∈ MultiPart.P M i
hj : j ∈ range (M.t + 1) ∧ j ≠ i
hk : k ∈ range (M.t + 1)
⊢ card
      ((move M hvi hj).A \
        if k ≠ i ∧ k ≠ j then MultiPart.P M k
        else if k = i then erase (MultiPart.P M i) v else insert v (MultiPart.P M j)) =
    if k ≠ i ∧ k ≠ j then card (M.A \ MultiPart.P M k)
    else if k = i then card (M.A \ MultiPart.P M i) + 1 else card (M.A \ MultiPart.P M j) - 1