theorem Th1: :: HESSENBE:1

for PCPP being CollProjectiveSpace
for a, b, c being Element of PCPP st a,b,c are_collinear holds
( b,c,a are_collinear & c,a,b are_collinear & b,a,c are_collinear & a,c,b are_collinear & c,b,a are_collinear )