koch curve
F 90 F 90 F 90 F
F -> F 60 F -120 F 60 F

quadratic koch island
F -90 F -90 F -90 F
F – > F -90 F 90 F 90 F F -90 F -90 F 90 F

F -90 F -90 F -90 F
F – > F F -90 F -90 F -90 F -90 F F

F -90 F -90 F -90 F
F – > F F -90 F +90 F -90 F -90 F F

F -90 F -90 F -90 F
F – > F F -90 F -90 -90 F -90 F

F -90 F -90 F -90 F
F – > F -90 F +90 F -90 F -90 F

Scheme source code:
l_system.scm
data.scm