Add attribute _x5_mult.
Modified _rankin_cohen_bracket_func.
moved _mul_q_half_monom.
Add class MultipleByX5.
Add _rankin_cohen_triple_mul_of_x5.
Add some functions for differential operators on x5.
Fix indentation.
Fix typo.
Modified _mul_q_half_monom.
Override method _differential_operator_monomial.
Add abstract class CommRingLikeElment.
Add FormalQexp. Deg2QsrsElement now inherits it.
Delete and add blank lines.
Modified common_prec.
Implement QseriesTimesQminushalf and ModFormQsrTimesQminushalf.
Modified Deg2QsrsElement.__mul__.
Implement ModFormQsrTimesQminushalf.__pow__.
add a test for multiplication of x5.
Override __getitem__ in QseriesTimesQminushalf.
Add _differential_operator_monomial.