∀ {α : Type u} {β : Type v} {x : BEq α} {x_1 : Hashable α} {m : Std.HashMap α β} [EquivBEq α] [LawfulHashable α]
  [inst : Inhabited β] {k a : α} {v : β}, (m.insert k v)[a]! = if (k == a) = true then v else m[a]!