Computability of Recursive Functions
Journal of the ACM (JACM)
Programming Approach to Computability
Programming Approach to Computability
The complexity of loop programs
ACM '67 Proceedings of the 1967 22nd national conference
From regulated rewriting to computing with membranes: collapsing hierarchies
Theoretical Computer Science
Computation: finite and infinite machines
Computation: finite and infinite machines
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We study the register complexity of LOOP-, WHILE-, and GOTO-programs, that is the number of registers (or variables) needed to compute certain unary (partial) functions from the non-negative integers to the non-negative integers. It turns out that the hierarchy of LOOP-computable (WHILE-, and GOTO-computable, respectively) functions f:ℕ0 →ℕ0 (partial functions $f:\mathbb{N}_0 \hookrightarrow \mathbb{N}_0$, respectively) that is induced by the number of registers collapses to a fixed level. In all three cases the first levels are separated. Our results show that there exist universal WHILE- and GOTO-programs with a constant number of registers.