Mame key mapping - "Not"

[danfman]

When I open up the options in Mame, and go to Input(General) or Input(This Game) I see configurations such as,
F7, Not Shift F7

How do I specify the "Not"?

[u_rebelscum]

Double click.

You first have to press at least one yes, then you can do the "not"s.

Example: to get "A not B", go to the right input, press enter, press 'A' key then quickly press the 'B' key twice.  Wait and see if mame got it.

edit: mameDev FAQ