exact hstart'
case hstart
β : Sort ?u.17044
α : Type u_1
f : β → α → β
b✝ : β
h : α → α → α
inst✝ : Std.Associative h
as : Array α
b c : α
start stop : Nat
hstart : start ≤ stop
hstop : stop ≤ as.size
hne : ¬start = stop
hstart' : start < stop
this : start < as.size
⊢ start < stop
no goals