Sat, 14 Feb 2009 16:51:18 -0800 huffman generalize lemma eq_neg_iff_add_eq_0, and move to OrderedGroup
(0) -10000 -3000 -1000 -300 -100 -30 -10 -1 +1 +10 +30 +100 +300 +1000 +3000 +10000 +30000 tip