Jörg> By sheer coincidence I just stumbled upon http://arxiv.org/abs/1105.3689 Can anyone comment on validity of the statements given? Best, jj This paper says "The symmetry identity [3, 4] and the trinomial revision identity [3, 4] are valid for all complex x,y,z" where [3] is G,K,&P's Concrete Math, which the author does not admit to contradicting. But GKP says "So the equation (-1 choose k) = (-1 choose -1-k) is always false! The symmetry identity fails for all other negative integers n, too. But unfortunately it’s all too easy to forget this restriction, since the expression in the upper index is sometimes negative only for obscure (but legal) values of its variables. Everyone who’s manipulated binomial coefficients much has fall into this trap at least three times." This paper is a fraud. --rwg