Chained list without head, problem in intersection function

I am doing a series of functions with list headless, but a function called Intersection is not working correctly, the problem compiles without errors but this function specifically does not run and the program presents runtime error, in that function must pass as parameter two list and the function returns a third list with the intersection of the two lists. Here is the code below:

#include<stdio.h>
#include<stdlib.h>

struct reg {
     int conteudo;
     struct reg *prox;
};

typedef struct reg celula;

void insere (celula **p, int x) {
     celula *novo, *q;
     q = *p;
     novo = (celula *)malloc(sizeof(celula));
     novo->conteudo = x;

     if (*p == NULL) {
          novo->prox = NULL;
          *p = novo;
     }

     else {
           while (q->prox != NULL)
                  q = q->prox;

           novo->prox = q->prox;
           q->prox = novo;
     }
}

void imprima (celula *p) {
     celula *q;
     if (p == NULL) printf ("Nao");
     else {
          for (q = p; q != NULL; q = q->prox)
                printf ("%d ", q->conteudo);
         printf ("\n");
      }
}

int NumElementos (celula *p) {
     celula *q;
     int n = 0;

     for (q = p; q != NULL; q = q->prox)
         n++;

return n;
}

int Pertence (celula *p, int x) {
     celula *q; int pt;
     q = p;

     while (q != NULL && q->conteudo != x)
           q = q->prox;

     if (q->conteudo == x) pt = 1;
     else pt = 0;

return pt;
}

celula *Interseccao (celula *p, celula *q) {
     celula *aq, *ap, *r = NULL;
     int aux;

     for (ap = p; ap !=NULL; ap = ap->prox) {
           for (aq = q; aq != NULL; aq = aq->prox) {
                aux = aq->conteudo;
                   if (Pertence(ap, aux) ==  1) {
                          if (Pertence(r, aux) == 0)
                                insere(&r, aux);
                 }
           }
      }
    return r;
}

int main () {
     celula *lista = NULL;
     celula *lst = NULL;
     celula *lis = NULL;

     int ne, p;

     insere (&lista, 8);
     insere (&lista, 2);
     insere (&lista, 1);
     insere (&lista, 3);
     insere (&lista, 9);
     imprima(lista);
     ne = NumElementos (lista);
     printf ("%d ", ne);
     p = Pertence(lista, 3);
     if (p == 0) printf("\n pertence");
     else printf("\npertence\n");
     insere (&lst, 7);
     insere (&lst, 3);
     insere (&lst, 5);
     insere (&lst, 1);
     imprima(lst);
     lis = Interseccao(lista, lst);
     imprima(lis);

return 0;
}