Hi, I defined some extra math symbols based on the help of David Munger. David posted a question 2 years ago, asking the group how to define extra math symbols. He found a solution himself (see below) and what I am trying to do is to put this into a math collection like math-eul.tex but I am not successfull. I used his solution to define a module math-extra.tex based on math-eul.tex but I am getting errors like ! \textfont 14 is undefined (character). \stopdisplaymath ->\stopinnermath $$ \ifgridsnapping \egroup \afterdisplayspa... \dostopformula ...eter \c!alternative \v!formula } \resetlastlinewidth \nonoi... l.18 \stopformula I don't know what I am doing wrong, hope someone can help me Attached my test files. Kind regards W. Neimeijer David's solution %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \definebodyfont [28pt,24pt,18pt, 17.3pt,14.4pt,12pt,11pt,10pt,9pt,8pt,7pt,6pt,5pt,4pt] [mm] [ ex=txex sa 1, mc=txexa sa 1, mrbf=cmbx10 sa 1, exbf=cmex10 sa 1, mibf=cmmib10 sa 1, sybf=cmbsy10 sa 1, mabf=msam10 sa 1] \setupbodyfont [12pt] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % txfonts %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \definemathsymbol [oiint] [op] [mc] ["08] [mc] ["09] \definemathsymbol [oiiint] [op] [mc] ["29] [mc] ["2a] \definemathsymbol [ointctrclockwise] [op] [mc] ["0A] [mc] ["0B] \definemathsymbol [ointclockwise] [op] [mc] ["0C] [mc] ["0D] \definemathsymbol [varointctrclockwise] [op] [mc] ["2B] [mc] ["2C] \definemathsymbol [varointclockwise] [op] [mc] ["2D] [mc] ["2E] \definemathsymbol [iint] [op] [mc] ["21] [mc] ["22] \definemathsymbol [iiint] [op] [mc] ["23] [mc] ["24] \definemathsymbol [iiiint] [op] [mc] ["25] [mc] ["26] \definemathsymbol [idotsint] [op] [mc] ["27] [mc] ["28] \definemathsymbol [oiintctrclockwise] [op] [mc] ["40] [mc] ["41] \definemathsymbol [oiintclockwise] [op] [mc] ["48] [mc] ["49] \definemathsymbol [varoiintctrclockwise][op] [mc] ["4A] [mc] ["4B] \definemathsymbol [varoiintclockwise] [op] [mc] ["42] [mc] ["43] \definemathsymbol [oiiintctrclockwise] [op] [mc] ["44] [mc] ["45] \definemathsymbol [oiiintclockwise] [op] [mc] ["4C] [mc] ["4D] \definemathsymbol [varoiiintctrclockwise][op] [mc] ["4E] [mc] ["4F] \definemathsymbol [varoiiintclockwise] [op] [mc] ["46] [mc] ["47] \starttext The integral equation \startformula \frac{d}{dt} \iiint_{\Omega} f \,dV = \iiint_{\Omega} Q \,dV - \oiint_{\partial\Omega} \vec J \cdot \vec{da} \stopformula can be written under the differential form \startformula \frac{\partial f}{\partial t} = Q - \vec\nabla\cdot\vec J. \stopformula \stoptext %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%