Thanks to the course given by Taco, I now know all about 'nil'... However, I did not track down the error, as Hans will find it immediately! Alan ! LuaTeX error ...beta/tex/texmf-context/tex/context/base/strc-lst.lua:195: bad argument #1 to 'gsub' (string expected, got nil) stack traceback: [C]: in function 'gsub' ...beta/tex/texmf-context/tex/context/base/strc-lst.lua:195: in function <...beta/tex/texmf-context/tex/context/base/strc-lst.lua:192> (tail call): ? ...beta/tex/texmf-context/tex/context/base/strc-lst.lua:392: in function 'analyze' <main ctx instance>:1: in main chunk. system > error on line 133 in file Livre.tex: LuaTeX error ... 133 >> \placepublications [criterium=all]