∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} {β : Type v} {m : Std.ExtDHashMap α fun x => β} [inst : EquivBEq α]
  [inst_1 : LawfulHashable α] [Inhabited α] {k k' : α} {f : β → β} {h : k' ∈ Std.ExtDHashMap.Const.modify m k f},
  (Std.ExtDHashMap.Const.modify m k f).getKey k' h = if (k == k') = true then k else m.getKey k' ⋯