apply Eq.trans
case h₂
a b✝ c✝ b c : ℕ
⊢ ((b + 1) * (a / (b + 1)) + a % (b + 1)) % ((b + 1) * (c + 1)) = (b + 1) * (a / (b + 1) % (c + 1)) + a % (b + 1)
case h₂.h₁
a b✝ c✝ b c : ℕ
⊢ ((b + 1) * (a / (b + 1)) + a % (b + 1)) % ((b + 1) * (c + 1)) = ?h₂.b

case h₂.h₂
a b✝ c✝ b c : ℕ
⊢ ?h₂.b = (b + 1) * (a / (b + 1) % (c + 1)) + a % (b + 1)

case h₂.b
a b✝ c✝ b c : ℕ
⊢ ℕ