code: def is_insert_grad_of_statement(node):
    
    tangent_calls = [anno.getanno(item.context_expr, 'func', None)
                     is utils.insert_grad_of for item in node.items]
    if all(tangent_calls):
      return True
    elif any(tangent_calls):
      raise ValueError
    else:
      return False
docs: Check whether a context manager calls `insert_grad_of`.
  
    Args:
      node: The context manager node.
  
    Returns:
      Whether or not this node contains `insert_grad_of` calls.
  
    Raises:
      ValueError: If the `insert_grad_of` calls are mixed with other calls.