Hi Hans and Taco, I want a command for writing prescript, something that works like ${}^1 f_t$ but with correct spacing. As far as I know, such a command does not exist in ConTeXt. A bit of a search shows that the "best" definition in LaTeX is by Michael J. Downes http://groups.google.com/group/comp.text.tex/msg/49206d0dffe71236?dmode=source&hl=en This is very similar to \lohi[left] but defined for math mode and takes care of math spacing. \DeclareRobustCommand{\prescript}[3]{% \@mathmeasure\z@\scriptstyle{#1}% put the sup in box 0 \@mathmeasure\tw@\scriptstyle{#2}% put the sub in box 2 \ifdim\wd\tw@>\wd\z@ \setbox\z@\hbox to\wd\tw@{\hfil\unhbox\z@}% \else \setbox\tw@\hbox to\wd\z@{\hfil\unhbox\tw@}% \fi % Do not let a preceding mathord symbol approach without any % intervening space. \mathop{}% % Use \mathopen to suppress space between the prescripts and the % base object even when the latter is not of type ord. \mathopen{\vphantom{#3}}^{\box\z@}_{\box\tw@}% #3% } To port it to ConTeXt, I need something equivalent to \@mathmeasure, which is defined in amsmath. % \begin{macro}{\@mathmeasure} % The function |\@mathmeasure| takes three arguments; the third arg % is typeset as a math formula in an hbox, using arg |#2| as the % mathstyle, and the result is left in the box named by the first % arg. It is assumed that we are already in math mode, so we can turn % off |\everymath| (in particular, |\check@mathfonts|). % \begin{macrocode} \def\@mathmeasure#1#2#3{\setbox#1\hbox{\frozen@everymath\@emptytoks \m@th$#2#3$}} What is the correct way to define mathmeasure in ConTeXt? I do not completely understand how math tokens are handled. Thanks, Aditya