congr 1
case left
α : Type u_1
as bs : Array α
start stop i : Nat
hstart : start ≤ stop
hstop : stop ≤ bs.size
hi : i < stop - start
ha : as.size + i < (foldl push as bs start stop).size
hb : start + i < bs.size
hne : ¬start = stop
hstart' : start < stop
this✝ : start < bs.size
this : as.size + i < (foldl push (as.push bs[start]) bs (start + 1) stop).size
⊢ (foldl push as bs start stop)[as.size + i] = (foldl push (as.push bs[start]) bs (start + 1) stop)[as.size + i]
case left.e_xs
α : Type u_1
as bs : Array α
start stop i : Nat
hstart : start ≤ stop
hstop : stop ≤ bs.size
hi : i < stop - start
ha : as.size + i < (foldl push as bs start stop).size
hb : start + i < bs.size
hne : ¬start = stop
hstart' : start < stop
this✝ : start < bs.size
this : as.size + i < (foldl push (as.push bs[start]) bs (start + 1) stop).size
⊢ foldl push as bs start stop = foldl push (as.push bs[start]) bs (start + 1) stop