∀ {α : Type u} {β : α → Type v} {x : BEq α} {x_1 : Hashable α} [inst : LawfulBEq α] {l : List ((a : α) × β a)}
  {k k' : α} (k_beq : (k == k') = true) {v : β k},
  List.Pairwise (fun a b => (a.fst == b.fst) = false) l → ⟨k, v⟩ ∈ l → (Std.DHashMap.ofList l).get? k' = some (cast ⋯ v)