Why isn't planar working for this quadrilateral?

 From:  Yenmonger (OTTERMAN)
1679.5 In reply to 1679.4 
Thanks Pilou. My real problem was lack of immersion into 3D. My 'top' and 'bottom' lines weren't parallel, and I had forgotten that 3, and only 3, lines define a plane.

Well, to be pendantic, there can be an arbitrary number of lines, as long as there are 3 non-parallel lines.