System T and the Product of Selection Functions

Martin Escardo, Paulo Oliva & Thomas Powell
We show that the finite product of selection functions (for all finite types) is primitive recursively equivalent to Goedel's higher-type recursor (for all finite types). The correspondence is shown to hold for similar restricted fragments of both systems: The recursor for type level n+1 is primitive recursively equivalent to the finite product of selection functions of type level n. Whereas the recursor directly interprets induction, we show that other classical arithmetical principles such as bounded...