∀ {α : Type u} {β : α → Type v} [inst : BEq α] [EquivBEq α] {l toInsert : List ((a : α) × β a)} {k : α},
  Std.Internal.List.DistinctKeys l →
    Std.Internal.List.DistinctKeys toInsert →
      ∀ {m : Std.Internal.List.containsKey k (Std.Internal.List.insertList l toInsert) = true}
        (contains : Std.Internal.List.containsKey k toInsert = true),
        Std.Internal.List.getKey k (Std.Internal.List.insertList l toInsert) m =
          Std.Internal.List.getKey k toInsert contains