∀ {α : Type u} {β : Type v} {m : Std.HashMap.Raw α β} [inst : BEq α] [inst_1 : Hashable α] [EquivBEq α]
  [LawfulHashable α], m.WF → ∀ {k a : α} {v : β}, (m.insert k v)[a]? = if (k == a) = true then some v else m[a]?