code: private static int  calcGap(AFP afp1 , AFP afp2)
  	{
  		int     g = (afp1.getP1() - afp2.getP1()) - (afp1.getP2() - afp2.getP2());
  		if(g < 0)       g = -g;
  		return g;
  	}
docs: return the gaps between this and afp
  requiring afp1 >  afp2
  ( operator % in C)