@techreport{plt-tr2008-turtles-v4.0, author = {PLT}, title = {Turtle Graphics}, number = {PLT-TR2008-turtles-v4.0}, type = {Reference Manual}, institution = {PLT Scheme Inc.}, month = {June}, year = {2008}, url = {http://download.plt-scheme.org/doc/4.0/pdf/turtles.pdf}, note = {\url{http://plt-scheme.org/techreports/}} }