Simplifications of the recursion scheme
M. D. Gladstone · Journal of Symbolic Logic · 1971
This paper resolves 3 problems left open by R. M. Robinson in [3]. We recall that the set of primitive recursive functions is the closure under (i) substitution (or “composition”), and (ii) recursion, of the set P consisting of the zero, successor and projection functions (see any textbook, for instance p. 120 of [2]).