Commit 2021-08-03 07:45 10216790

feat(algebra/ordered_monoid): a few more order_dual instances (#8519)

• add covariant.flip and contravariant.flip;
• add [to_additive] to group.covariant_iff_contravariant and covconv (renamed to group.covconv);
• use group.covconv in group.covariant_class_le.to_contravariant_class_le;
• add some order_dual instances for covariant_class and contravariant_class;
• golf order_dual.ordered_comm_monoid.