∀ {α : Type u} {β : α → Type v} [inst : BEq α] [inst_1 : LawfulBEq α] {l toInsert : List ((a : α) × β a)} {k : α}
  (not_contains : (List.map Sigma.fst toInsert).contains k = false)
  {h : Std.Internal.List.containsKey k (Std.Internal.List.insertList l toInsert) = true},
  Std.Internal.List.getValueCast k (Std.Internal.List.insertList l toInsert) h = Std.Internal.List.getValueCast k l ⋯