rem: return 1;
add: return true;
context: recurse_tree (struct item *root, int (*action) (struct item *)){  if (root->left == NULL && root->right == NULL)    return (*action) (root);  else    {      if (root->left != NULL)	if (recurse_tree (root->left, action))	  return 1;      if ((*action) (root))	return 1;      if (root->right != NULL)	if (recurse_tree (root->right, action))	  return 1;    }  return 0;}