really stupid simple maths keyboard command question

[Owen Lucas]

When in maths mode you can press meta-m and it allows you to type in 
commands as shown in maths.bind. I can get the single character options 
to work but cant get the multiple ones to key in. in the file maths.bind 
these multi character commands start with. "~S-" I assume that you need 
to press or hold a key down a key first. what is it?

cheers
owen