∀ {α : Type u} {β : Type v} {x : BEq α} {x_1 : Hashable α} [inst : EquivBEq α] [inst_1 : LawfulHashable α]
  {l : List (α × β)} {k k' : α},
  (k == k') = true →
    ∀ {v : β},
      List.Pairwise (fun a b => (a.1 == b.1) = false) l →
        (k, v) ∈ l → ∀ {h : k' ∈ Std.ExtHashMap.ofList l}, (Std.ExtHashMap.ofList l)[k'] = v