# Cubic Bézier interpolation between `a` and `b` with two handles using `self` as weight
	#
	# The Cubic Bézier interpolation is the most common one and use two control points.
	#
	# ~~~
	# assert  0.00.cerp(0.0, 32.0, 128.0, 64.0) == 0.0
	# assert  0.25.cerp(0.0, 32.0, 128.0, 64.0) == 32.5
	# assert  0.50.cerp(0.0, 32.0, 128.0, 64.0) == 68.0
	# assert  0.75.cerp(0.0, 32.0, 128.0, 64.0) == 85.5
	# assert  1.00.cerp(0.0, 32.0, 128.0, 64.0) == 64.0
	# ~~~
	fun cerp(a, a_handle, b_handle, b: Float): Float do
		var p = self
		var i = 1.0 - p
		var r =     i*i*i  * a +
			3.0*i*i*p * a_handle +
			3.0*i*p*p * b_handle +
			    p*p*p * b
		return r
	end