The inverse of the Ackermann function grows very slowly but is not primitive recursive. That is, the function f where f(n) is the smallest m such that A(m) exceeds n. Of course, this is hardly a different method of proof.
The inverse of the Ackermann function grows very slowly but is not primitive recursive. That is, the function f where f(n) is the smallest m such that A(m) exceeds n. Of course, this is hardly a different method of proof.