DFN_NAN
parentp -> toporder = DFN_NAN;
if ( parentp -> toporder == DFN_NAN ) {
parentp -> toporder = DFN_NAN;
cyclenlp -> toporder = DFN_NAN; /* graph call chain top-sort order */
return ( childp -> toporder != DFN_NAN && childp -> toporder != DFN_BUSY );
if ( childp -> toporder == DFN_NAN ) {
dfn_counter = DFN_NAN;