The routine returns true if the two given line are skew; false if they are not; and FAIL if it is unable to reach a conclusion.

The command with(geom3d,AreSkewLines) allows the use of the abbreviated form of this command.

$\mathrm{with}\left(\mathrm{geom3d}\right)\:$

$\mathrm{line}\left(\mathrm{l1}\,\left[\mathrm{point}\left(\mathrm{A1}\,0\,0\,0\right)\,\mathrm{point}\left(\mathrm{A2}\,1\,1\,0\right)\right]\right)$

$\mathrm{l1}$

$\mathrm{line}\left(\mathrm{l2}\,\left[\mathrm{point}\left(\mathrm{B1}\,0\,0\,1\right)\,\mathrm{point}\left(\mathrm{B2}\,1\,-1\,1\right)\right]\right)$

$\mathrm{l2}$

$\mathrm{AreSkewLines}\left(\mathrm{l1}\,\mathrm{l2}\right)$

$\mathrm{true}$

$\mathrm{AreParallel}\left(\mathrm{l1}\,\mathrm{l2}\right)$

$\mathrm{false}$