Alt key ignored, 4.2.12, on MacBook Pro 64

[MarcGirod]

Hello,

How to make the Alt key(s) accessible to the guest (ubuntu 12.04)?
I selected an English (UK, Macintosh) keyboard, which is what I found closest to my MacBook, but of the modifier keys, only ctrl (and Left cmd) are recognized.
I tried with xev, and no event gets recorded when I press alt.
On my bottom row, I have: fn, ctrl, alt, cmd, space bar, cmd, alt

Thanks,
Marc

[MarcGirod]

Sorry,
Once again, after posting my question, found the answer myself...
Found the Modifier Keys entry under Keyboard settings, i.e. where I ought to have expected to find it...
Thanks,
Marc