for N being invertible Matrix of 3,F_Real
for h being Element of SubGroupK-isometry
for n11, n12, n13, n21, n22, n23, n31, n32, n33 being Element of F_Real
for P being Element of BK_model
for u being non zero Element of (TOP-REAL 3) st h = homography N & N = <*<*n11,n12,n13*>,<*n21,n22,n23*>,<*n31,n32,n33*>*> & P = Dir u & u . 3 = 1 holds
((n31 * (u . 1)) + (n32 * (u . 2))) + n33 <> 0