A = (-1, 0)
B = (5, 1)
C = (1, 3)
D = (-3, 1)
poly1, a, b, c, d = Polygon(A, B, C, D)
e = Line(A, C)
f = Line(B, D)
g = Line(A, f)
h = Line(B, e)
i = Line(C, f)
j = Line(D, e)