This paper describes the class of functions on natural numbers that can be obtained from some well-known functions (arithmetical and bitwise that used in programming) by superposition with the following restriction: formula may have no more than 2 floors. It’s proved that this class coincides with a modification of the class of Skolem elementary functions (also known as “lower elementary recursive functions”).

Recursive functions, superposition bases, substitution bases

Mathematical problems and theory of numerical methods