typedef struct node list;
typedef NULL END;

bool is_circular(list l)
{
        a=l.head;
        b=(a->next)->next;

        while((b != END) && (a != b))
        {

                if((b == l) || (a == l)) {
                   /*
                   ** Perfect circular, as per the standard definition.
                   */
                   return 1;
                }

                if (END != b->next) {
                   b=(b->next)->next;
                }
                else {
                   /*
                   ** The list is a linear one.
                   */
                   return 0;
                }
                a=a->next;
        }

        if (END == b) {
           return 0;  //Linear case.
        }
        else { 
           /*
           ** Some kind of loop
           */
           return 1; 
        }

}