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1995 J. Phys. A: Math. Gen. 28 2217
L.D.Fadeev and R.M.Kashaev, Quantum Dilogarithm, Mod. Phys. Lett. A. 9 (1994) p.427–434
qdilog.pdf
http://ncatlab.org/nlab/show/quantum+dilogarithm