FormWriter
	opportunity
	problem
	goals
	related-work
	turtle_geometry
	flying_turtle
	formwriter_screen
	formwriter_language
	simple_examples
	islamic_geometry
	discussion
	future_work
	thanks

describing a circle

differential
parametric	for t = 0 to 360 x = r cos (t) y = r sin (t)
cartesian	for x = -r to r y = ± sqrt (r^2 - x^2)