∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} [EquivBEq α] [LawfulHashable α] {l : List α} {k k' fallback : α},
  (k == k') = true →
    List.Pairwise (fun a b => (a == b) = false) l → k ∈ l → (Std.HashMap.unitOfList l).getKeyD k' fallback = k