[Tex/LaTex] Extensible double angle, etc

math-mode

I was wondering about an efficient way to generate an inner product symbol like 

\[
\langle\langle u, v \rangle\rangle
\]

(i.e., double angle brackets), or a norm symbol like 

\[
\lvert\lVert x \rVert\rvert
\]

(i.e., triple bars). Of course, the above examples are terrible, no respect for spaces. Is there an efficient way of doing this so that the delimiters are extensible (compatible with $\left$ and $\right$)?

I know of the package nath, but it's quite incompatible with amsmath, and generates thousands of errors, so is not an option. I've also tried with "DeclareMathDelimiterX" in mathmode, but couldn't get it to work quite as well as I'ld like.

Best Answer

Strangely enough, Detexify didn't help here. Another great source is The Comprehensive LaTeX Symbol List, and this has the following answers:

For your first delimiter pair use \llangle and \rrangle from the mnsymbol package (as observed in Martin's comment above); for the second pair you can try \vvvert from mathabx.

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