∀ {α : Type u} {β : α → Type v} [inst : BEq α] [PartialEquivBEq α] {l : List ((a : α) × β a)} {k a : α} {v : β k},
  Std.Internal.List.containsKey a (Std.Internal.List.insertEntryIfNew k v l) = true →
    ¬((k == a) = true ∧ Std.Internal.List.containsKey k l = false) → Std.Internal.List.containsKey a l = true