rw [card_eq_sum_ones, sum_mul, one_mul]
case e_a
t : ℕ
P : ℕ → ℕ
h : Balanced t P
f : ℕ → ℕ
⊢ ∑ x in largeParts h, f (P x) = card (largeParts h) * f (minP t P + 1)
case e_a
t : ℕ
P : ℕ → ℕ
h : Balanced t P
f : ℕ → ℕ
⊢ ∑ x in largeParts h, f (P x) = ∑ x in largeParts h, f (minP t P + 1)