adj_vertex_t *tour( adj_vertex_t *E, adj_vertex_t *P){
    if (count_vertices(P) == graphSize){
        return (P);
    }
    adj_vertex_t *inter = setIntersection(E, P);
    if (inter == NULL){
        return NULL;
    }
    adj_vertex_t *v;
    adj_vertex_t *result;
    for(v=inter; v != NULL; v = v->next) {
        result = tour(v->vertex->adj_list, setUnion(P, v));
    if(result) {
        free_adj_list(result);
        return result;
    }
}

adj_vertex_t *setUnion(adj_vertex_t *A, adj_vertex_t *B){
    adj_vertex_t *result = malloc(sizeof(adj_vertex_t));
    adj_vertex_t *res_current = result;
    adj_vertex_t *adj_v;
    for (adj_v = A; adj_v != NULL; adj_v = adj_v->next, res_current = res_current->next) {
        res_current->vertex = adj_v->vertex;
        res_current->weight = adj_v->weight;
        res_current->next = malloc(sizeof(adj_vertex_t));
    }
}