Snaps invoked by keystroke

When using the 'Measure Distance' command, and at other times, when

about to place a data or tentative point, I would like to choose a snap,

by keystroke. In the popup snaps list, the names of the snaps have their

first character capitalised and underlined, which conventionally leads me

to hold down 'Alt' while hitting the key corresponding to the underlined capital

letter, eg I hit Alt-I for intersect., but nothing happens.

How can the purportedly available keyboard strokes be enabled?

I think they are enabled in the middle of the 'stretch' command.

thanks for any help

Jim