Hi Matthias,
This is generally not a good idea: WR_ (subscripted) is seen as:
Times[Blank[],Subscript[W,R]]
while WR_ (no subscript) is seen as:
Pattern[WR,Blank[]]
Which are fundamentally different. Moreover, the first argument of Pattern must be a symbol, i.e. not something with a Head different from Symbol (e.g. Subscript). Try not to use subscripts in Mathematica, it doesn't work very nice. See for example:
r=2;
r+Subscript[r, a]
outputs:
2+Subscript[2, a]
I.e. the ra (subscript) is seen as variable r with a subscript, not a new variable by itself.
