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This is a subquestion related to Evaluation Symbol.

Is there something of the form \left<?> instead of \left. telling LaTeX to enclose the expression here and not to insert any delimiter at all, no matter wether visible or invisible?

As an example I want:

\left<no-delimiter><stuff>\right|_<index>

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C-star-W-star
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    Can you clarify your question, I can not guess what input or output you intend. If you do not want any delimiter why do you need any markup at all? – David Carlisle Dec 11 '14 at 09:55
  • Of course, a moment, please. – C-star-W-star Dec 11 '14 at 09:57
  • looking at the referenced question it seems that you want \left. but after setting \nulldelimiterspace=0pt Is that a correct interpretation of your question? – David Carlisle Dec 11 '14 at 09:57
  • YES!! But doesn't . stand for spacing. Does there exist \nulldelimiter? – C-star-W-star Dec 11 '14 at 10:02
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    \newcommand\noleft{\left.\kern-\nulldelimiterspace} – egreg Dec 11 '14 at 10:02
  • There is no csname for the nulldelimiter just use . but the amount of space is configurable – David Carlisle Dec 11 '14 at 10:25
  • @DavidCarlisle: Btw does it read null'delimiterspace or nulldelimiter'space? Does . really mean nodelimiter? – C-star-W-star Dec 11 '14 at 10:31
  • @Freeze_S I'm not sure I understand the distinction you make, the TeXbook says: A null delimiter isn't completely void; it is an empty box whose width is a TeX parameter called \nulldelimiterspace. We will see later that null delimiters are inserted next to fractions. Plain TeX sets \nulldelimiterspace=1.2pt. – David Carlisle Dec 11 '14 at 10:41
  • @DavidCarlisle: Ah ok, so it is really the null delimiter not just a delimiter with null space around it, thanks!! – C-star-W-star Dec 11 '14 at 21:18

3 Answers3

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When \left. is used, TeX inserts no delimiter, but adds a space of width \nulldelimiterspace. It's not advisable to set this parameter to zero, in my opinion. But with

\newcommand{\noleft}{\left.\kern-\nulldelimiterspace}

using

\noleft x\right|_{a}

will in any case remove the added space.

As explained in my answer to the referenced question, using a macro would be much better for ensuring consistency. If your aim is to get code that works also with MathJax out of the box, you're on the wrong road: the capabilities of MathJax are limited and so you are forcing yourself into using bad LaTeX.

egreg
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<stuff>\big|_<index>

is also possible. There is also \Big, \bigg, and \Bigg

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\usepackage{mleftright}
\[ x \mleft. \frac{1}{2} \mright|_i ]|

The package mleftright fixes the spacing of \left. and \right|, so that it is the same as in $ x \frac{1}{2} |_x $ but the | vertically stretches as you were using \left. and \right|.

So \mleft. should do what you do (null delimiter, no space), but consider that the space after \mright| is reduced too.

Taekwondavide
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