The Borel Hierarchy Theorem from Brouwer's intuitionistic perspective
Wim Veldman · Journal of Symbolic Logic · 2008
Abstract In intuitionistic analysis, Brouwer's Continuity Principle implies, together with an Axiom of Countable Choice, that the positively Borel sets form a genuinely growing hierarchy: every level of the hierarchy contains sets that do not occur at any lower level.