That is an excellent question. I've only seen capital pi used for repeated multiplication. I, too, would like to know what it means in this context. I don't

That is an excellent question. I've only seen capital pi used for repeated multiplication. I, too, would like to know what it means in this context. I don't know if you missed it, but the author links to a PDF that mentions this notation in the abstract. I haven't had a chance to digest it, though: http://www.cs.cmu.edu/~crary/819-f09/Murthy91.pdf http://www.cs.cmu.edu/~crary/819-f09/Murthy91.pdf Edit: Behold... http://en.wikipedia.org/wiki/Descriptive_set_theory http://en.wikipedia.org/wiki/Descriptive_set_theory http://en.wikipedia.org/wiki/Arithmetical_hierarchy http://en.wikipedia.org/wiki/Arithmetical_hierarchy http://en.wikipedia.org/wiki/Analytical_hierarchy http://en.wikipedia.org/wiki/Analytical_hierarchy