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