alignement professeur
Author: stage de mathématiques Aquitaine

A = (0, 0)
B = (4, 0)
C = (4, 4)
D = (0, 4)
poly1, a, b, c, d = Polygon(A, B, C, D)
y_I = 2.55 (slider from 0 to 4, step 0.05)
I: (2.0, y_I)
poly2, b_1, a_1, i = Polygon(A, I, B)
J: (4.0 + y_I, 2.0)
poly3, b_2, c_1, j = Polygon(C, J, B)
u = Vector(D, I)
v = Vector(D, J)