sum of rings

[Oleksandr]

the sum of rings should better give at least warning about equal variable names, consider for instance:

> ring r; r;
//   characteristic : 32003
//   number of vars : 3
//        block   1 : ordering dp
//                  : names    x y z
//        block   2 : ordering C
> ring s; s;
//   characteristic : 32003
//   number of vars : 3
//        block   1 : ordering dp
//                  : names    x y z
//        block   2 : ordering C
> def R = r + s; setring R; R;
//   characteristic : 32003
//   number of vars : 3
//        block   1 : ordering dp
//                  : names    x y z
//        block   2 : ordering C

should give a warning on

> def R = r + s; setring R; R;

[seelisch]

question by Gert-Martin Greuel in the meeting of Feb 12, 2009, added by Frank Seelisch: Is there anything to check for the non-commutative case? --> Hans, please reassign to Oleksandr Motask after investigation on usefulness of above warning.