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