Thu, 03 Nov 2011 11:18:06 +0100 huffman ex/Tree23.thy: prove that insertion preserves tree balance and order
(0) -30000 -10000 -3000 -1000 -300 -100 -30 -10 -1 +1 +10 +30 +100 +300 +1000 +3000 +10000 +30000 tip