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LaTeX: curly braces!

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    Writing \{ a,b,c \} in TeX doesn't work on mathoverflow. Neither does \left\{ a,b,c \right\}. Neither does \left{ a,b,c \right}. All that appears is a,b,c. I'm quite surprised and appalled by this situation. (See my question on exchangeable normal r.v.s.)
    • CommentAuthorvoloch
    • CommentTimeSep 7th 2011
     
    Try \lbrace a,b,c \rbrace .
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    @voloch: Thank you. I figured that out a minute after I posted above. Do most people know that? I had long thought that the usual thing was \{ \}. (Or \left\{ and \right\} if you want the delimiter sizes to match what they enclose.) It's annoying to wrestle with things like that when you're trying to think about the content you're posting.
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    This is due to the fact that the Markdown interpreter doesn't know about MathJaX. So it doesn't ignore stuff between dollars. Since it uses the backslash to escape special characters, it translates \{ to { (and \\ to a single backslash, and similar for other things). Then MathJaX only sees { which it interprets as a TeX group and so doesn't display the brace. One solution is to use \lbrace and \rbrace as voloch says. Another is to put the mathematics inside an HTML tag so that Markdown doesn't look at it. If the paragraph doesn't contain anything else that Markdown should look at, you can just put <p> ... </p> around it.

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    (And, of course, Markdown demonstrated my point by escaping the angle brackets in those tags!)

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    Or you could use backticks, but perhaps Andrew will scold me for bad practice.

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    Yes!

    Anton now says that backticks are bad practice since the behaviour will not be stable under changes to the software. The fact that Markdown doesn't look inside block-level tags is part of the specification of Markdown so anything that pretends to be Markdown has to accept that. But Markdown does look inside backticks and what it does there can depend on the configuration.

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    Thanks for that Andrew. :) I shall use \lbrace ... \rbrace from now on.

    • CommentAuthorEmil J
    • CommentTimeSep 8th 2011
     
    Oh god, I always found backticks to be the single most useful Markdown command. What about \\{ \\}, are they stable or not?

    And how does the thing with HTML tags work, exactly? I just tried <p>$\{0,1\}$</p> and <div>$\{0,1\}$</div> in answer preview, and neither works (even though the tags are recognized: the <p> started a separate paragraph).
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    I wouldn't worry too much about backticks. They are rather convenient for most people, and if we're ever faced with a breaking change we can think about regex tricks to ameliorate the problems.

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