I'm looking for a way to get the following done

I want to have a command


with the following definition

\def\setcitation#1#2{\lowercase{\expandafter\gdef\csname mycommoncitation#1\endcsname}{#2}}

Essentially, what it does is each time it is called with arguments xXx and yyy, it creates a new command


defined as


Now, given an input, xxX, I would like to get yyy out. So what has to happen: convert xxX to lowercase xxx, call \mycommoncitationxxx

I tried doing this as follows:


And as follows:

\newcommand\getcitation[1]{\lowercase{\expandafter\gdef\csname mycommoncitation#1\endcsname}}

However niether work.

For the first part (the definition of my setcitation command) I based my solution on build a capitalized CS from a lowercase string and to give it a definition

For the second part, I don't find any help yet.

Complete example, that also shows how I want to use these commands:



\getcitationifexistsotherwiseinput{Foo} %My expectation: Bar
\getcitationifexistsotherwiseinput{foo} %my expectation: Bar
\getcitationifexistsotherwiseinput{boo} %my expectation: boo
%Now I want a command that returns 
% \getcitation{FOO} 

\cite{\getcitation{foo}} %my expectaiton: "undefined citation Bar"

here, in the line \cite{...} things start to go wrong.

  • 1
  • lowercase is not expandable so does not work inside \cite if you don't mind enumerating all the letters (eg if you only allow a-z, not accented letters) then it is possible to write an expandable version. Or simpler use a modified command say \lccite that applies lowercase then \cite` Jan 20, 2017 at 13:57
  • The problem with that is that I cometimes want to use it in the form \cite{something,\getcitation{somethingelse}}, SO I'ld basically ahve to patch the entire cite command...
    – BartBog
    Jan 20, 2017 at 14:51
  • @BartBog well then you can use the expandable lowercase commands in the question that Steven linked Jan 20, 2017 at 15:43

2 Answers 2


You need an expandable version of \lowercase:


  \prop_gput:Nxn \g_bartbog_citations_prop { \str_lowercase:n { #1 } } { #2 }
  \prop_item:Nf \g_bartbog_citations_prop { \str_lowercase:n { #1 } }

\cs_generate_variant:Nn \prop_gput:Nnn { Nx }
\cs_generate_variant:Nn \prop_item:Nn { Nf }
\prop_new:N \g_bartbog_citations_prop





\bibitem{Bar} Whatever



I used a property list for compactness.

enter image description here

  • When I try this, I get a lot of LaTeX Warning: Citation `' on page 1 undefined on input line 28. errors and getctation does not print anything...
    – BartBog
    Jan 25, 2017 at 9:25
  • Also: could you extend your answer with a command like getcitationifexistsotherwiseinput in my question. It is not clear to me how to check existance in explsyntax
    – BartBog
    Jan 25, 2017 at 9:28
  • @BartBog What are you expecting? You're passing something to \cite which it doesn't know. What can be done is making the message something like LaTeX Warning: Citation `MISSING' on page 1 undefined on input line 28, not much more.
    – egreg
    Jan 25, 2017 at 12:05
  • What I mean is that when I run exactly your code, I don't get Bar Bar Bar [1] [1] [1] but [?] [?] [?]. I.e., it does not seem to be working. Concretely, if I remove the \str_lower_case:n from getcitation, One of the \getcitations works...
    – BartBog
    Jan 25, 2017 at 12:23
  • @BartBog Are you sure you have an up-to-date TeX system?
    – egreg
    Jan 25, 2017 at 12:25

I just posted another answer to Expandably change letter case and use inside \csname, without a package.

That answer can be found at https://tex.stackexchange.com/a/349895/118714 .

That answer contains a routine \UD@ExpandableLowercase which delivers lowercasing of those 26 catcode-11(letter)-character-tokens that correspond to the 26 letters of the latin alphabet within two expansion steps. That routine does not require eTeX or the like extensions.

(!!!Be aware that having TeX read and tokenize input consisting of characters of the latin alphabet usually yields catcode-11(letter)-character tokens while expanding \string, \meaning, \jobmane and the like primitives delivers catcode-12(other)-character-tokens!!!)

As a (probably disliked) side effect that routine does replace pairs of matching catcode-1-character-tokens and catcode-2-character-tokens by pairs of matching curly catcode-1-brace-tokens and curly catcode-2-brace-tokens, i.e. { and }.

I think this should not be a problem with plain TeX and LaTeX2e as with these formats usually the only character with category code 1 is the opening curly brace { and the only character with category code 2 is the closing curly brace }.

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