@ARTICLE{DasVas_j2011_a, author = {J{\"u}rgen~Dassow and Gy{\"o}rgy~Vaszil}, title = {On the Number of Active Symbols in {L}indenmayer Systems}, journal = ijfcs, year = 2011, volume = {22}, number = {1}, pages = {223--235}, url = {http://dx.doi.org/10.1142/S0129054111007976} }