"FM" == Frank Mittelbach writes: FM> for "symbols" like the above this can in fact be done this way FM> and a few symbols hare "historically defined this way, ie FM> \pounds -> \relax\ifmmode\mathsterling\else\textsterling FM> but you need the \relax to ensure that the right thing happens at FM> the beginning of tabular cells (timing problem in \halign) FM> and this is the problem: you can't do that to "letters", the use FM> of \relax there prohibits potential ligatures and not doing it FM> means your definition produce wrong results or blow up in certain FM> situations there is a solution for this problem used in the mathtext package available from CTAN:macros/latex/contrib/supported/t2/etc/mathtext.{dtx,ins} this package is referred to as experimental in the doculentation of the cyrillic latex bundle. the approach used in the mathtext package proved to be stable enough: i know a lot of people do use it for `transparent' cyrillic letters in math, and i did not hear about bug for a long time now. the mechanism mostly works on a fontenc layer, rather than on inputenc. so, something like this could be used to make even `letters' work in both modes (however, mathtext currently only redefines \DeclareTextSymbol, which is sufficient for cyrillic, but to make it work for T1 font encoding, one needs to extend redefinitions of other commands like composite declarations, etc). Best regards, -- Vladimir.