On Sat, 06 Sep 2008 00:33:25 -0400, Manu Hack wrote: > Actually it's even more natural to state sum([x]) = x, and this way you > can never conclude that sum([]) = 0 from there. But what you can say is that for any list L, sum(L) = sum(L + [0]). Therefore sum([]) = sum([] +[0]) = 0 -- Steven