from matplotlib import pyplot

def TRACER_POINT(x1, y1) :
    pyplot.plot([x1], [y1], color='blue', marker='+') 
def F1(x) :
	return x**3 - x**2

xdepart=-2
while (xdepart<=4) :
	TRACER_POINT(xdepart,F1(xdepart))
	xdepart=xdepart+pas
pyplot.show()