[1XReferences[0X [[20XEGN[15X] [16XEick, B., G\"ahler, F. and Nickel, W.[15X, [17Xcryst[15X, \URL{http://www.gap-system.org/Packages/cryst.html} [[20XEll[15X] [16XEllis, G.[15X, [17XHAP[15X, \URL{http://hamilton.nuigalway.ie/Hap/www/} -------------------------------------------------------