# Redefining \left \right

I have already asked a part of this question in the following post:

Math Time Professional

I fell that I am not content with the answer for this part (as I will explain why). I am using MTPro2 and to get large parenthesis or brackets one needs to use the following commands

  \LEFTRIGHT(){Math Formula},    \LEFTRIGHT\{\}{Math Formula}


I don't want to use these commands and instead I would like to use \left(Math Formula\right) and \left\{ Math Formula \right\}. The reason being that I would like to submit my papers and many journals don't support MTPro2 so I want to use \left(Math Formula\right) or \left\{ Math Formula \right\} instead of \LEFTRIGHT(){Math Formula} to prevent retyping my papers.

So now my question is, how can I define a macro that takes \left(Math Formula\right) and produces \LEFTRIGHT(){Math Formula} for me?

PS: As egreg suggested I can define \providecommand\LEFTRIGHT[3]{\left#1#3\right#2} my goal is to know how one can change the LaTeX code and redefine these comments hoping to learn more LaTeX programming.

• Isn't it easier to define \LEFTRIGHT when you remove mtpro2? – egreg Apr 27 '18 at 22:26
• You might be under the impression that \left and \right are LaTeX commands taking an argument (in the LaTeX sense of the word), but they aren’t: they are primitive commands of the underlying TeX engine. – GuM Apr 27 '18 at 23:55
• It basically is not feasible to redefine \left and \right to support that syntax. – David Carlisle Apr 28 '18 at 7:22
• GuM has already pointed out that \left and \right are primitives. really, all you will learn by trying to redefine them is that it's a mistake to try to redefine a primitive. – barbara beeton Apr 28 '18 at 19:08

You should do it the other way around:

\documentclass{article}

\usepackage[lite]{mtpro2}

\providecommand\LEFTRIGHT[3]{\left#1#3\right#2}

\begin{document}

$\LEFTRIGHT(){\sum_{k=0}^n k}=\frac{n(n+1)}{2}$

\end{document}


If you comment out the call to mtpro2, you get

I find neither a particularly good way to typeset the formula.

• Thanks for your answer, which is nice and correct, but my goal is more to learn how to redefine \left and \right. – MO B Apr 27 '18 at 22:47
• @MOB I wouldn't undertake the task even for money. – egreg Apr 27 '18 at 22:48