Dear list, Sorry for the stupid title, I couldn't resist. :-) LuaTeX has the option to adjust spacing between different classes of math atoms. However, looking in the TeXbook, page 170, in the table for spacings between adjacent atoms, we find that some of those spacing are undefined (* in the table) and therefore, when TeX encounters this combination, spacing is just skipped. This also translates to the parameters in LuaTeX. For example the combination Open-Bin is skipped by TeX and therefore setting the corresponding parameter just does nothing. \Umathordrelspacing\textstyle=50mu \Umathopenbinspacing\textstyle=50mu $a = (-2)$ \bye So my question is, what is the point of the parameters that describe these skipped combinations? Shouldn't they just be deleted? Alternatively, they could actually be implemented to do something. More context: https://tex.stackexchange.com/questions/532758 Kind regards, Henri