def case_1(node):
    """ Case when node have two children, one
    of which is operator, other not.
    In that case choice operator node as top node.
    
    Example:
    T->[a, *->[a]] to *->[a, a]"""
    op_node = node.find_op_child()
    unop_node = node.find_unop_child()
    op_node.add_child(unop_node)
    parent = node.parent
    if parent is not None:
        parent.replace_child(node, op_node)
        return parent
    else:
        op_node.parent = parent
        return op_node
