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How to look up a symbol?

How does one make the symbol for a blackboard bold kind square brackets ,something like [[.The symbol being talked about is used for containing formulas whose truth values are being talked about in propositional logic. Thanks and regards An image of the symbol: enter image description here

marked as duplicate by lockstep, Loop Space, egreg, percusse, Claudio Fiandrino Nov 7 '12 at 13:49

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  • the symbol i am talking about is something like [[ squeezed together to form one symbol used in propositional logic. e.g \tau [[phi]]=1 – heboy Nov 7 '12 at 10:21
  • Finding an image on Google Images might help users determine the exact symbol you're referring to. – dunc Nov 7 '12 at 10:37
  • i have edited the question and added an image of the symbol. – heboy Nov 7 '12 at 10:47
  • If you use unicode-math, you can just use the Unicode characters ⟦ (U+27E6) and ⟧ (U+27E7). They work nicely with \big and \left/\right and the like. (Sadly I cannot post this as an answer.) – Marian Apr 10 at 15:52

You are looking for

  • \llbracket and \rrbracket from the stmaryrd package
  • \textlbrackdbl and \textrbrackdbl from the textcomp package

Detexify is an online tool that can help you find latex symbols by drawing them.


  • 3
    If I could've upvoted more than once, I would've. – Vatine Nov 7 '12 at 10:51
  • Detexify is great. It worked fine even with my limited drawing skills. – lhf Nov 7 '12 at 11:38

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