Are there existing LaTeX commands \1,\2,\3, or \4?

Question

I want to make new commands with the names \1 \2 \3 \4. But I do not want to use these names if they will conflict with standard existing names. I do not know of any existing LaTeX commands with these names but I want to check.

This is exactly what \newcommand is for: it will allow the definition as they do not exist. — Joseph Wright, May 29 '17 at 20:01
@JosephWright But I will use these in many files which do not yet exist, and i do not want to create an unintended conflict later on. — Colin McLarty, May 29 '17 at 20:03
I know of two packages that define \0, \1, \2: qtree and tikz-qtree-compat. — Alan Munn, May 29 '17 at 20:05
Related/duplicate: How can I check in LaTeX (or plain TeX) whether a command exists, by name? — Werner, May 29 '17 at 20:10
@Werner That is about a way to control macro expansion within a document and alter its run depending on what command names exist at that time. I just want to know for myself if these names are in use. Indeed Alan Munn points out they are, which I wish they weren't, so I have to decide what to do. — Colin McLarty, May 29 '17 at 20:19
@AlanMunn That answers my question and if you post it as an answer I will accept. Maybe it is not decisive for my purposes since I do not so far use tikz to draw trees, but I do use tikz. — Colin McLarty, May 29 '17 at 20:23

score 9 · Accepted Answer · edited May 29 '17 at 21:20

a rough estimate can be found just by looking for \[0-9] in the latex/*/*.sty files in your local installation.

eg

$ grep '[^`\\]\\[0-9]' /usr/local/texlive/2017/texmf-dist/tex/latex/*/*.sty | grep -v Digits

Just keeping one line per package and removing comments and uses with \string returns the following list, some of which will be internal uses, but each would need to be checked.

/arabtex/hebchrs.sty:\ifx #1\relax \relax \else \uppercase {\gdef \1{#1}}%
/bengali/beng.sty:\def\3#1z{{\char"#1}}
/bibarts/bibarts.sty:   \def\3{\string\3}%
/biblatex/biblatex.sty:  \do\0\do\1\do\2\do\3\do\4\do\5\do\6\do\7\do\8\do\9%
/cbcoptic/coptic.sty:\let\0\^^b0 % alias name for keyboards missing the "degree" key
/cmdtrack/cmdtrack.sty:\ifcat ?$\relax{\catcode37=7 \catcode127=9 \def\0{\@sanitize\catcode}\fi
/cryptocode/cryptocode.sty:      { \1\u{l_pc_strsub_replace_tl} }
/csquotes/csquotes.sty:  \do\!\do\?\do\0\do\1\do\2\do\3\do\4\do\5\do\6\do\7\do\8\do\9}
/cuisine/cuisine.sty:  \let\0\d@grees
/dialogl/grabhedr.sty:  \edef\0{\meaning\input}\edef\1{\string\input}%
/dialogl/menus.sty:  \begingroup \def\0{?}\def\1{Q}%
/dvdcoll/pdfnotiz.sty:    \edef\0{\string\0}%
/etextools/etextools.sty:   \long\edef\1##1/##2/##3{##1\endgroup\unexpanded{#2}##3}%
/fonttable/fonttable.sty: \f@tm=\f@tn \divide\f@tm by 64 \xdef\0{\the\f@tm}%
/gmdoc/gmdoc.sty:    \DoNotIndex{\1 \2 \3 \4 \5 \6 \7 \8 \9 \0}%
/hyperref/hyperref.sty:    \edef\1{\string\1}%
/longfigure/longfigure.sty:  \begingroup\def\2{#2}
/media9/media9.sty:    \regex_replace_once:nnN{([^:]+):??.*}{\1}\l_tmpa_tl
/mftinc/mftinc.sty:\long\def\mfcomment#1\9#2\par{\unskip#2 }
/mhchem/mhchem.sty:        { \c{\\}(\[.*?\])? } { \0 }
/nicetext/niceverb.sty:      \def\cs{\134}%                    %% 2010/03/17, 2011/06/27
/outlines/outlines.sty:%   \1 <level 1 text>
/pdfx/pdfx.sty: \edef\0{\string\0}
/pkgloader/pkgloader.sty:       \c{g__pkgloader_pkg_graph}\cB\{\0\.sty\cE\}) }
/prftree/prftree.sty:  \global\prf@samefalse\begingroup\def\1{#1}\def\2{#2}%
/proba/proba.sty:\DeclareRobustCommand{\1}[1]{\ensuremath \mathbf{1}_{\{#1\}}}
/protex/AlProTex.sty:   \def\1{#1}%
/qsymbols/qsymbols.sty:  \expandafter\let\expandafter\1\csname qsym@@#1\endcsname
/qtree/qtree.sty:  \def\0{\ifmmode ^0\else \rlap{$^0$}\fi}%
/regexpatch/regexpatch.sty:      \regex_replace_once:nnN { .*? \{ (.*) \} \Z } { \1 }
/snapshot/snapshot.sty:      \edef\0{\csname rqv@#1\endcsname}%
/songs/songs.sty:  \let\2\1\let\3\1\let\4\1\let\5\1%
/teubner/teubner.sty:\def\2#1 {\csname2#1\endcsname}
/tikz-qtree/tikz-qtree-compat.sty:  \def\0{\ifmmode ^0\else \rlap{$^0$}\fi}%
/toptesi/topfront.sty:        \ifx\2\empty
/toptesi/topfront.sty:            \noexpand\oldstylenums{\1} -- \noexpand\oldstylenums{\2}}
/uaclasses/my-title.sty:    {\def \1{#1}%
/uaclasses/ua-title.sty:    {\edef \3{#1}%
/ucs/ucshyper.sty:      \edef\1{\string\1}%
/units/units.sty:    \def\0{#1}%
/velthuis/dev209.sty:\def\0{\llap{\char13}}
/velthuis/devanagari.sty:\DeclareRobustCommand*\0{\llap{\char13}}%

@JosephWright if I knew a regular expression to filter out regular expression replacements I'd add it to that grep call:-) adding |grep -v regex to the end of the pipeline might be near enough:-) — David Carlisle, May 29 '17 at 22:09

Are there existing LaTeX commands \1,\2,\3, or \4?

1 Answers1