Przemyslaw Prusinkiewicz Jim Hanan Radomír Mech An L-System-Based Plant Modeling Language. 395-410 http://link.springer.de/link/service/series/0558/bibs/1779/17790395.htm 1999 conf/agtive/1999 AGTIVE db/conf/agtive/agtive1999.html#PrusinkiewiczHM99