# Is the angle between [p1,p2] and [p2,p3] going left (counter clockwise) or right (clockwise) ?
#
# ~~~
# var p1 = new Point[Float](0.0, 0.0)
# var p2 = new Point[Float](5.0, 0.0)
# var p3 = new Point[Float](0.0, 5.0)
# assert turn_left(p1, p2, p3)
# ~~~
fun turn_left(p1, p2, p3: Point[Float]): Bool do
	return ((p2.x - p1.x) * (p3.y - p2.y) - (p3.x - p2.x) * (p2.y - p1.y)) > 0.0
end