R1 = (1, 13)
R2 = (21, 11)
S1 = (1, 4)
S2 = (21, 6)
T1 = (8, 15)
T2 = (5, 2)
U1 = (15, 15)
U2 = (12, 2)
a = Segment(R1, R2)
b = Segment(S1, S2)
c = Segment(T1, T2)
d = Segment(U1, U2)