How to add variable arguments to \newcommand inside \SetBreakableRel from the package rmathbr? (inline math-break with repetition)

Question

rmathbr is a package enabling another convention of breaking inline equations if they run too long. Specifically, symbols are repeated on the new line (and kept on previous line). So, for instance, a = b is broken as on a = on the first line and = b continuing on the second line. The package was recently updated (December 2020).

• Please consider using that newest version when attempting to answer the question; otherwise unexpected bugs may be present.

There is a macro called \SetBreakableRel in the rmathbr package to create compound symbols one would also like to break with duplication when necessary (see documentation). For example, to get a breakable , one defines a new command \goesto as (in the document preamble)

\newcommand{\goesto}{\xrightarrow{n\to\infty}}
\SetBreakableRel{\goesto}

This works great as far as I am concerned (line is broken and symbol is duplicated):

$e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e$ gives

The problems begin when one tries to define new commands (which break and duplicate) that also take in variable arguments. For example, if instead of n and ∞ one wants to have variables #1 and #2, i.e

\newcommand{\goestoarg}[2]{\xrightarrow{#1\to#2}} %<-- this doesn't work
\SetBreakableRel{\goestoarg} %<-- this doesn't work

then this gives errors and does not work: for example, $\goestoarg{a}{b}$ just gives (this is the wrong symbol to begin with so I didn't attempt to see if it duplicates on line break). To show that the problem is likely from rmathbr: if one (only) comments out \SetBreakableRel{\goestoarg}, one has the expected output: . But, of course, I want to have it uncommented to enforce line breaking with duplication for this relation \goestoarg.

• Question: How does one define \goestoarg with two arguments so that it works properly with \SetBreakableRel?

I have also tried to put two #'s (that is, ## instead of #, see MWE below) to no avail.

---

Here is the code (with some additional packagages to hint at needed compatibility with other packages):

\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[LGR,T1]{fontenc}
\usepackage[english]{babel}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{mathtools}
\usepackage{titlesec}
\usepackage{rmathbr}
\usepackage[pdftex]{graphicx}
\usepackage{parskip}
\usepackage[a4paper]{geometry}

\newcommand{\goesto}{\xrightarrow{n\to\infty}} %works great
\SetBreakableRel{\goesto} %works great

%%%%% uncomment as necessary

%\newcommand{\goestoarg}[2]{\xrightarrow{#1\to#2}} %<-- this doesn't work
%\SetBreakableRel{\goestoarg} %<-- this doesn't work

%\newcommand{\Goestoarg}[2]{\xrightarrow{##1\to##2}} %<-- this also doesn't work
%\SetBreakableRel{\Goestoarg} %<-- this also doesn't work


\begin{document}


$e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e$

%$\goestoarg{a}{b}$ %<- does not work
%$\Goestoarg{a}{b}$ %<- also does not work


\end{document}

---

Here is the log file from when \goestoarg stuff (three lines: the definition, SetBreakableRel and usage $\goestoarg{a}{b}$) is uncommented. This is a subset of the entire log file; I narrowed it down to start when rmathbr is loaded because the 30 000 character limit was exceeded. The errors are just before TeX Memory usage output near the end of the log.

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/rmathbr\rmathbr.st
y
Package: rmathbr 2020/12/18 1.1.1 Repeating of math operator at the broken line
 and the new line in inline equations

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/generic/iftex\ifetex.sty
Package: ifetex 2019/10/25 v1.3 ifetex legacy package. Use iftex instead.
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/generic/iftex\iftex.sty
Package: iftex 2020/03/06 v1.0d TeX engine tests
))
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/generic/iftex\ifluatex.s
ty
Package: ifluatex 2019/10/25 v1.5 ifluatex legacy package. Use iftex instead.
)
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/xkeyval\xkeyval.st
y
Package: xkeyval 2020/11/20 v2.8 package option processing (HA)

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/generic/xkeyval\xkeyval.
tex
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/generic/xkeyval\xkvutils
.tex
\XKV@toks=\toks30
\XKV@tempa@toks=\toks31
)
\XKV@depth=\count271
File: xkeyval.tex 2014/12/03 v2.7a key=value parser (HA)
))
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/l3kernel\expl3.sty
Package: expl3 2021-02-18 L3 programming layer (loader) 

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/l3backend\l3backen
d-pdftex.def
File: l3backend-pdftex.def 2021-03-18 L3 backend support: PDF output (pdfTeX)
\l__color_backend_stack_int=\count272
\l__pdf_internal_box=\box51
)))
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/graphics\graphicx.
sty
Package: graphicx 2020/09/09 v1.2b Enhanced LaTeX Graphics (DPC,SPQR)

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/graphics\graphics.
sty
Package: graphics 2020/08/30 v1.4c Standard LaTeX Graphics (DPC,SPQR)

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/graphics\trig.sty
Package: trig 2016/01/03 v1.10 sin cos tan (DPC)
)
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/graphics-cfg\graph
ics.cfg
File: graphics.cfg 2016/06/04 v1.11 sample graphics configuration
)
Package graphics Info: Driver file: pdftex.def on input line 105.

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/graphics-def\pdfte
x.def
File: pdftex.def 2020/10/05 v1.2a Graphics/color driver for pdftex
))
\Gin@req@height=\dimen164
\Gin@req@width=\dimen165
)
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/parskip\parskip.st
y
Package: parskip 2021-03-14 v2.0h non-zero parskip adjustments

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/kvoptions\kvoption
s.sty
Package: kvoptions 2020-10-07 v3.14 Key value format for package options (HO)

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/generic/ltxcmds\ltxcmds.
sty
Package: ltxcmds 2020-05-10 v1.25 LaTeX kernel commands for general use (HO)
)
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/generic/kvsetkeys\kvsetk
eys.sty
Package: kvsetkeys 2019/12/15 v1.18 Key value parser (HO)
))
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/etoolbox\etoolbox.
sty
Package: etoolbox 2020/10/05 v2.5k e-TeX tools for LaTeX (JAW)
\etb@tempcnta=\count273
))
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/geometry\geometry.
sty
Package: geometry 2020/01/02 v5.9 Page Geometry

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/generic/iftex\ifvtex.sty
Package: ifvtex 2019/10/25 v1.7 ifvtex legacy package. Use iftex instead.
)
\Gm@cnth=\count274
\Gm@cntv=\count275
\c@Gm@tempcnt=\count276
\Gm@bindingoffset=\dimen166
\Gm@wd@mp=\dimen167
\Gm@odd@mp=\dimen168
\Gm@even@mp=\dimen169
\Gm@layoutwidth=\dimen170
\Gm@layoutheight=\dimen171
\Gm@layouthoffset=\dimen172
\Gm@layoutvoffset=\dimen173
\Gm@dimlist=\toks32

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/geometry\geometry.
cfg))
No file Test12.aux.
\openout1 = `Test12.aux'.

LaTeX Font Info:    Checking defaults for OML/cmm/m/it on input line 27.
LaTeX Font Info:    ... okay on input line 27.
LaTeX Font Info:    Checking defaults for OMS/cmsy/m/n on input line 27.
LaTeX Font Info:    ... okay on input line 27.
LaTeX Font Info:    Checking defaults for OT1/cmr/m/n on input line 27.
LaTeX Font Info:    ... okay on input line 27.
LaTeX Font Info:    Checking defaults for T1/cmr/m/n on input line 27.
LaTeX Font Info:    ... okay on input line 27.
LaTeX Font Info:    Checking defaults for TS1/cmr/m/n on input line 27.
LaTeX Font Info:    ... okay on input line 27.
LaTeX Font Info:    Checking defaults for OMX/cmex/m/n on input line 27.
LaTeX Font Info:    ... okay on input line 27.
LaTeX Font Info:    Checking defaults for U/cmr/m/n on input line 27.
LaTeX Font Info:    ... okay on input line 27.
LaTeX Font Info:    Checking defaults for LGR/cmr/m/n on input line 27.
LaTeX Font Info:    Trying to load font information for LGR+cmr on input line 2
7.

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/cbfonts-fd\lgrcmr.
fd
File: lgrcmr.fd 2017/07/29 v1.2 Greek European Computer Regular
)
LaTeX Font Info:    ... okay on input line 27.

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/context/base/mkii\supp-p
df.mkii
[Loading MPS to PDF converter (version 2006.09.02).]
\scratchcounter=\count277
\scratchdimen=\dimen174
\scratchbox=\box52
\nofMPsegments=\count278
\nofMParguments=\count279
\everyMPshowfont=\toks33
\MPscratchCnt=\count280
\MPscratchDim=\dimen175
\MPnumerator=\count281
\makeMPintoPDFobject=\count282
\everyMPtoPDFconversion=\toks34
)
(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/epstopdf-pkg\epsto
pdf-base.sty
Package: epstopdf-base 2020-01-24 v2.11 Base part for package epstopdf
Package epstopdf-base Info: Redefining graphics rule for `.eps' on input line 4
85.

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/00miktex\epstopdf-
sys.cfg
File: epstopdf-sys.cfg 2021/03/18 v2.0 Configuration of epstopdf for MiKTeX
))
*geometry* driver: auto-detecting
*geometry* detected driver: pdftex
*geometry* verbose mode - [ preamble ] result:
* driver: pdftex
* paper: a4paper
* layout: <same size as paper>
* layoutoffset:(h,v)=(0.0pt,0.0pt)
* modes: 
* h-part:(L,W,R)=(89.62709pt, 418.25368pt, 89.6271pt)
* v-part:(T,H,B)=(101.40665pt, 591.5302pt, 152.11pt)
* \paperwidth=597.50787pt
* \paperheight=845.04684pt
* \textwidth=418.25368pt
* \textheight=591.5302pt
* \oddsidemargin=17.3571pt
* \evensidemargin=17.3571pt
* \topmargin=-7.86334pt
* \headheight=12.0pt
* \headsep=25.0pt
* \topskip=12.0pt
* \footskip=30.0pt
* \marginparwidth=44.0pt
* \marginparsep=10.0pt
* \columnsep=10.0pt
* \skip\footins=10.8pt plus 4.0pt minus 2.0pt
* \hoffset=0.0pt
* \voffset=0.0pt
* \mag=1000
* \@twocolumnfalse
* \@twosidefalse
* \@mparswitchfalse
* \@reversemarginfalse
* (1in=72.27pt=25.4mm, 1cm=28.453pt)

LaTeX Font Info:    Trying to load font information for U+msa on input line 30.

(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/amsfonts\umsa.fd
File: umsa.fd 2013/01/14 v3.01 AMS symbols A
)
LaTeX Font Info:    Trying to load font information for U+msb on input line 30.


(C:\Users\Lala\AppData\Local\Programs\MiKTeX 2.9\tex/latex/amsfonts\umsb.fd
File: umsb.fd 2013/01/14 v3.01 AMS symbols B
)
! Argument of \rmathbr@orig@goestoarg has an extra }.
<inserted text> 
                \par 
l.32 $\goestoarg{
                 a}{b}$ %<- does not work
? 
Runaway argument?
! Paragraph ended before \rmathbr@orig@goestoarg was complete.
<to be read again> 
                   \par 
l.32 $\goestoarg{
                 a}{b}$ %<- does not work
? 
! Missing $ inserted.
<inserted text> 
                $
l.32 $\goestoarg{
                 a}{b}$ %<- does not work
? 
! Missing } inserted.
<inserted text> 
                }
l.32 $\goestoarg{
                 a}{b}$ %<- does not work
? 
! Too many }'s.
<recently read> }
                 
l.32 $\goestoarg{
                 a}{b}$ %<- does not work
? 
! Missing $ inserted.
<inserted text> 
                $
l.34 
     
? 
[1

{C:/Users/Lala/AppData/Local/MiKTeX/2.9/pdftex/config/pdftex.map}]
(Test12.aux) ) 
Here is how much of TeX's memory you used:
 7565 strings out of 479283
 112372 string characters out of 2852377
 434818 words of memory out of 3000000
 24941 multiletter control sequences out of 15000+600000
 408839 words of font info for 46 fonts, out of 8000000 for 9000
 1141 hyphenation exceptions out of 8191
 68i,16n,75p,1197b,108s stack positions out of 5000i,500n,10000p,200000b,80000s
{C:/Users/Lala/AppData/Local/Programs/MiKTeX 2.9/fonts/enc/dvip
s/cm-super/cm-super-t1.enc}<C:/Users/Lala/AppData/Local/Programs/MiKTeX 2.9/f
onts/type1/public/amsfonts/cm/cmmi12.pfb><C:/Users/Lala/AppData/Local/Program
s/MiKTeX 2.9/fonts/type1/public/amsfonts/cm/cmmi8.pfb><C:/Users/Lala/AppData/
Local/Programs/MiKTeX 2.9/fonts/type1/public/amsfonts/cm/cmsy10.pfb><C:/Users/R
asmus/AppData/Local/Programs/MiKTeX 2.9/fonts/type1/public/amsfonts/cm/cmsy8.pf
b><C:/Users/Lala/AppData/Local/Programs/MiKTeX 2.9/fonts/type1/public/cm-supe
r/sfrm1200.pfb>
Output written on Test12.pdf (1 page, 36772 bytes).
PDF statistics:
 27 PDF objects out of 1000 (max. 8388607)
 0 named destinations out of 1000 (max. 500000)
 1 words of extra memory for PDF output out of 10000 (max. 10000000)

---

I am running pdflatex 3.141592653-2.6-1.40.22 (MikTeX 21.3), and every package in my local distrubution was updated earlier today.

Answer 1

Only minimally tested, but this should work. There may be a reason why this is not suggested in the documentation, but I haven't been able to reason out when something like this should fail to work.

\documentclass[12pt]{article}
%\usepackage[utf8]{inputenc}
%\usepackage[english]{babel}
\usepackage{amsmath}
%\usepackage{amssymb}
%\usepackage{amsthm}
\usepackage{mathtools}
\usepackage[pdftex]{graphicx}
%\usepackage{titlesec}
\usepackage{rmathbr}
%\usepackage{parskip}
%\usepackage[a4paper]{geometry}

\newcommand{\goesto}{\xrightarrow{n\to\infty}} %works great
\SetBreakableRel{\goesto} %works great

\DeclareRobustCommand{\goestoarg}[2]{\brokenrel{\xrightarrow{#1\to#2}}}

\begin{document}


$e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e\goesto e$

$e\goestoarg{a}{b} e \goestoarg{a}{b} e \goestoarg{a}{b} e \goestoarg{a}{b} e \goestoarg{a}{b} e \goestoarg{a}{b} e \goestoarg{a}{b} e \goestoarg{a}{b} e \goestoarg{a}{b} e \goestoarg{a}{b} e \goestoarg{a}{b} e \goestoarg{a}{b} e \goestoarg{a}{b} e $ 
%$\Goestoarg{a}{b}$ %<- also does not work


\end{document}