The algebraic uniqueness of the addition of natural numbers. Elemer E. Rosinger (1982) Aequationes mathematicae
The limit lemma in fragments of arithmetic Vítězslav Švejdar (2003) Commentationes Mathematicae Universitatis Carolinae The recursion theoretic limit lemma, saying that each function with a 𝛴 n + 2 graph is a limit of certain function with a 𝛥 n + 1 graph, is provable in B Σ n + 1 .
The role of rudimentary relations in complexity theory Hugo Volger (1984) Mémoires de la Société Mathématique de France
The word problem in polycyclic groups is elementary F. B. Cannonito, R. W. Gatterdam (1973) Compositio Mathematica