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 : 05/22/18-04:00:03 AM Z CEST