struct Node {
  int value;
  unsigned int pnx;
};
unsigned int XOR(struct Node* a, struct Node* b){

  return  (unsigned int)a ^ (unsigned int)b;

}
struct Node* insert_first(int value, struct Node* next){

  struct Node *node = (struct Node*) malloc(sizeof(struct Node));
  node->value = value;

  node->pnx = XOR(next, NULL);
  if(next != NULL){
    next->pnx = XOR( node, (struct Node*)next->pnx);
  }
  return node;
}



int main(){

  struct Node* node = insert_first(3, NULL);
  node = insert_first(4, node);

  struct Node* next= (struct Node*) XOR( (struct Node*)node->pnx, NULL);

  struct Node* prev= (struct Node*) XOR( (struct Node*)next->pnx, NULL);

  printf("%d %u\n", node->value, node->pnx);
  printf("%d %u\n", next->value, next->pnx);
  printf("%d %u\n", prev->value, prev->pnx);
  //  print_list(node);

  return 0;
}