theorem :: EUCLID_6:49

for c1, c2, c3 being Element of COMPLEX holds
( (angle (c1,c2)) + (angle (c2,c3)) = angle (c1,c3) or (angle (c1,c2)) + (angle (c2,c3)) = (angle (c1,c3)) + (2 * PI) ) by Lm14;