List * zeroPredList;
        List * list;
        List retList;
        Int * count;
        int num_Nodes, index, value, pred, succ;

        if (fscanf(idata, "%d", &num_Nodes) == EOF) {
                printf("Number of nodes is inaccessible.\n");
                return NULL;
        }

        zeroPredList = makeList(sizeofInt(), copyInt, free);
        list = (List *)calloc(num_Nodes, sizeof(List));

        index = 0;
        /* Make a list for each node for successor/predecessor upkeep */
        while (index < num_Nodes) {
                list[index] = makeList(sizeofInt(), copyInt, free);
        }

        /* Pred count of succ is incremented and succ goes in pred list */
        while (fscanf(idata, "%d %d", &pred, &succ) != EOF) {
                count[succ]++;
                insertTail(list[pred], &succ);
        }

        index = 0;
        /* Put items with no pred into zero-pred list */
        while (index < num_Nodes) {
                if (count[index] == 0) {
                        insertTail(zeroPredList, &index);
                }
                index++;
        }

        /* Remove item k from zero-pred list and output record. Traverse
           k successor list and decrement the count for each record found.
           If record j count is set to zero, then include j on the zero-pred
           list. Continue until zero-pred list is emtpy */

while (deleteTail(zeroPredList, &value)) {

                /* Push zero-pred items onto the returned list */
                insertTail(retList, &value);
                Int temp;
                while (deleteTail(list[value], temp)) {
                        count[valueInt(temp)]--;
                        if (count[valueInt(temp)] == 0) {
                                insertTail(zeroPredList, &temp);
                        }
                }
        }


        return retList;