revert haxs
case a
α : Type u
r : α → α → Prop
inst✝¹ : StrictLinearOrder r
inst✝ : DecidableRel r
β : α → Type v
f : (a : α) → β a → β a → Option (β a)
xs : KVChain r β
a : α
b : β a
ys : KVChain r β
hays : boundLeft a ys
haxs : boundLeft a xs
⊢ (insertWithAux f KVChain.nil xs True.intro a b True.intro).val =
    ({ toList := [{ fst := a, snd := b }],
        ascend := (_ : List.Ascending (Sigma.relOnFst (flip r)) [{ fst := a, snd := b }]) },
      xs)
case a
α : Type u
r : α → α → Prop
inst✝¹ : StrictLinearOrder r
inst✝ : DecidableRel r
β : α → Type v
f : (a : α) → β a → β a → Option (β a)
xs : KVChain r β
a : α
b : β a
ys : KVChain r β
hays : boundLeft a ys
⊢ boundLeft a xs →
    (insertWithAux f KVChain.nil xs True.intro a b True.intro).val =
      ({ toList := [{ fst := a, snd := b }],
          ascend := (_ : List.Ascending (Sigma.relOnFst (flip r)) [{ fst := a, snd := b }]) },
        xs)