@article {1292, title = {Polylog space compression, pushdown compression, and Lempel-Ziv are incomparable}, journal = {Theory of Computing Systems}, volume = {48}, year = {2011}, pages = {731-766}, url = {http://webdiis.unizar.es/~elvira/research.html}, author = {E. Mayordomo and P. Moser and S. Perifel} }