function void
push(Type *l, Type *node){
  if(l->first == 0){
    l->first = l->last = node;
    node->prev = 0;
    node->next = 0;
  }
  else{
    l->last->next = node;
    node->prev = l->last;
    node->next = 0;
    l->last = node;
  }
  node->parent = l;
}

function void
push_front(Type *l, Type *node){
  if(l->first == 0){
    l->first = l->last = node;
    node->prev = 0;
    node->next = 0;
  }
  else{
    node->next = l->first;
    l->first->prev = node;
    node->prev = 0;
    l->first = node;
  }
  node->parent = l;
}

function void
remove(Type *l, Type *node){
  if(l->first == l->last){
    assert(node == l->last);
    l->first = l->last = 0;
  }
  else if(l->last == node){
    l->last = l->last->prev;
    l->last->next = 0;
  }
  else if(l->first == node){
    l->first = l->first->next;
    l->first->prev = 0;
  }
  else{
    node->prev->next = node->next;
    node->next->prev = node->prev;
  }
  
  node->parent = 0;
  node->prev = 0;
  node->next = 0;
}