theorem Th28: :: SEMI_AF1:28

for SAS being Semi_Affine_Space
for a, b, c, d, x being Element of SAS st not a,b,c are_collinear & a,b // c,d & c <> d & c,d,x are_collinear holds
not a,b,x are_collinear by Th8, Th27;