He's asked me how to include the umlaut for Möbius in postscript, any ideas?

I'm not sure what this means. What did you use to produce the slides? if you compose a TeX manuscript containing only M\"obius\end the umlaut appears correctly in the resulting Postscript files. I have attached Postscript files produced in two different ways (mob2.ps is frm TeX and dvips and mob2ps1.ps is from PDFTeX and Preview). The essential [Joerg Arndt's message just arrived but since I didn't understand it, I decided to continue writing anyawy] bit seems to be /Encoding 256 array 0 1 255 {1 index exch /.notdef put} for dup 49 /one put dup 77 /M put dup 98 /b put dup 105 /i put dup 111 /o put dup 115 /s put dup 117 /u put dup 127 /dieresis put in the first and /Encoding 256 array 0 1 255 {1 index exch /.notdef put} for dup 33 /M put dup 34 /dieresis put dup 35 /o put dup 36 /b put dup 37 /i put dup 38 /u put dup 39 /s put dup 40 /one put in the second. If you omit the umlaut in the TeX manuscript, the line that goes away is the one with /dieresis, so I beleive that produced the umlaut. Joerg seems to have indicated how you might edit your postscript to produce the right result. The thrust of my comment is that it is probably a matter of what program you used to produce the Postscript. (I see that it came from Ghostscript but I don't see what is above that.) Whit