I am using
FreeQ to define a replacement rule. However, it doesn't seem to be possible to specify a list of variables as the second argument, which is why I came up with something like this
AngleBracket[a_ b_] := a AngleBracket[b] /; (FreeQ[a, x] && FreeQ[a, y] && FreeQ[a, z])
Now, for many variables
x,y,z, ... this becomes very tedious. Is there a better, i.e., shorter way to achieve what I want?