Abstract

Given two internal sets X and Y we prove that every Borel function whose graph is a subset of the product X x Y is a member of the least set containing the class of all internal functions and closed with respect to the operations of monotone countable union and intersection. We also prove that any Souslin function can be extended to a Borel function and obtain, as a corollary, a new proof of the recent result of Henson and Ross about the measure preserving property of injective Souslin functions. Further we give a new proof of the fact that injective Borel functions map Borel sets into Borel. A structural result for Souslin graphs all of whose Y-sections are of cardinality n is given