code: private static int parity(IAtom[] atoms) {
          return parity(atoms[0].getPoint2d(), atoms[1].getPoint2d(), atoms[2].getPoint2d());
      }
docs: Determine the parity (odd/even) of the triangle formed by the 3 atoms.
  
  @param atoms array of 3 atoms
  @return the parity of the triangle formed by 3 points, odd = -1, even =
  +1