Thank you very much!!!
Now that I understood that the $MUs are just dummy indeces I also found another solution that gets rid of them:
ToExpression[StringReplace[ToString[Calc[M] // StandardForm], "$MU" -> "a"]]
Again, thanks for your quick reply!!!
This archive was generated by hypermail 2b29 : 04/20/18-06:20:01 PM Z CEST