simp[this]
f : ℕ → ℕ →. ℕ
hf : ArithPart₁ fun v => f (v.get 0) (v.get 1)
n : ℕ
g h : Vector ℕ n → ℕ
hg : Arith₁ g
hh : Arith₁ h
i : Vector ℕ n
this : (fun j => ![↑g, ↑h] j i) = fun j => pure (![g i, h i] j)
⊢ ((mOfFn fun i_1 => ![↑g, ↑h] i_1 i).bind fun v => f v.head (v.get 1)) = f (g i) (h i)
no goals