rw [foldl_stop]
case e_xs
α : Type u_1
as bs : Array α
start stop i : Nat
hstart : start ≤ stop
hstop : stop ≤ bs.size
hi : i < as.size
h : i < (foldl push as bs start stop).size
heq : start = stop
⊢ foldl push as bs stop stop = as
case e_xs.hstop
α : Type u_1
as bs : Array α
start stop i : Nat
hstart : start ≤ stop
hstop : stop ≤ bs.size
hi : i < as.size
h : i < (foldl push as bs start stop).size
heq : start = stop
⊢ stop ≤ bs.size