HoTT/book — pull request #324 by loopspace (2013-06-25 13:02:16+00:00)
Title: Change 1^\mathsf{W} to 1^{\mathfs{W}} 

The superscript and subscript tokens don't behave quite like ordinary macros in that things like 1^\mathsf{W} works. If ^ were a macro, which took one argument, this wouldn't work as the ^ would get \mathsf as its argument and the {W} would be left outside. Changing this to 1^{\mathsf{W}} makes no difference to the final typeset material but does mean that it is possible to make ^ into a macro, which is necessary for conversion to ePub.