 vertices are the 3-element
      subsets of the set of vectors:

         ( 0, 0, 0 )
         ( 1, 0, 0 )
         ( 0, 1, 0 )
         ( 0, 0, 1 )

      function pltvol_t

         %
         % Let the notation
         %
         %    &lt; A, B &gt;
         %
         % denote the dot product of vectors A and B.
         %
         % The plates defined below lie in the following planes,
         % respectively:
         %
         %    Plate 1:    { P :  &lt; P, (-1,  0,  0) &gt; = 0 }
         %    P