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up vote 9 down vote favorite

What is the character obtained with they key sequence Esc,Esc called? On my front end it is not displayed, but there's something there messing up my input. It's a bit annoying when I'm after a $\mu$ but hit the wrong key.

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Thanks for the answers guys. I'd just like to note that despite what the help says, [InvisibleComma] does not play nice with ordinary commas. – wxffles Feb 7 '12 at 18:51
Ah, I see what you mean. {a, b, c} is fine, {a\[InvisibleComma] b\[InvisibleComma] c} is fine, but {a\[InvisibleComma] b, c} isn't. Very peculiar... – J. M.♦ Feb 8 '12 at 0:10
Thanks a lot! (I'll delete my comments in a few.) – J. M.♦ yesterday

2 Answers

up vote 15 down vote accepted

It's what's called an \[InvisibleComma]. It's useful for those times where you don't want a comma to appear, but you still need it, e.g. "a[[p\[InvisibleComma]q]]" for a matrix entry.

screenshot

The third entry uses an \[InvisibleComma] in between the matrix indices.

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2  
ah. the man himself :) – acl Feb 7 '12 at 1:09
up vote 8 down vote

The next time you wonder what a symbol is you can at least partially answer it yourself by entering it in a string wrapped in FullForm:

Mathematica graphics

(this is just before pressing Esc the second time). You would get:

"\[InvisibleComma]"

Which is surely helpful in some way. You can also get the help page for the character by entering it directly into the help search box:

Mathematica graphics

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3  
Or just enter the original input described (Esc,Esc), select the cell, and look at its underlying expression -- on Mac, Shift+Cmd+E. – murray Feb 8 '12 at 20:28
@murray good suggestion, though I think the Box structure is a little confusing to a new user. – Mr.Wizard♦ Feb 8 '12 at 21:35

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