乗法的不定和分
http://reference.wolfram.com/mathematica/ref/Product.html -Indefinite products with Mathematica
http://www.math.rwth-aachen.de/MapleAnswers/660.html - bug in Maple V to Maple 8 handling of indefinite product
Markus Müller. How to Add a Non-Integer Number of Terms, and How to Produce Unusual Infinite Summations
Markus Mueller, Dierk Schleicher. Fractional Sums and Euler-like Identities