def case_3_1(node):
    """ Case when node have two children, one
    of which is brackets, other not (W->[a, )] or E->[(, a]).
    In that case it transform from:
    T->['(', H->[args, ')']]
    to
    br->['(', args, ')']"""
    parent = node.parent
    grandparent = parent.parent
    arg_node = node.find_unbr_child()
    br_r_node = node.find_br_child()
    node.remove_child(br_r_node)
    node.remove_child(arg_node)
    parent.remove_child(node)
    parent.add_child(arg_node)
    parent.add_child(br_r_node)
    parent.name = 'br'
    parent.visited = True
    if grandparent is not None:
        return grandparent
    else:
        return parent
