\begin{array}{} Lorsque\;  les\;  diagonales\;  ont\;  le\;  même \; milieu, \;\le\; quadrilatère\; est\; un\; parallélogramme.\end{array}  

A = (5.98, 2.64)
B = (-6, 2.66)
C = (1.82, -3.58)
D = (8.32, -0.7)
q1, a, b, c, d = Polygon(A, B, C, D)
M = Midpoint(A, C)
N = Midpoint(D, B)
f = Segment(C, M)
g = Segment(M, A)
h = Segment(B, N)
i = Segment(N, D)
e = false