I would like to create a vertical "evaluation" bar similar to the one in this formula:
This was produced by the code:
df\,_{\big\rvert x} \colon T_x M \to T_y N
It comes close to what I want, but I am not entirely satisfied: I would like the 'x' to be lower (e.g. aligned with the bottom of the vertical bar). Also maybe have the vertical bar slightly less tall.
Suggestions? Thank you!