src/Pure/Thy/latex.ML

     ("|", "{\\isacharbar}"),
     ("}", "{\\isacharbraceright}"),
     ("~", "{\\isachartilde}")];
 
 fun output_chr " " = "\\ "
+  | output_chr "\t" = "\\ "
   | output_chr "\n" = "\\isanewline\n"
   | output_chr c =
       (case Symtab.lookup char_table c of
         SOME s => enclose_literal c s
       | NONE => if Symbol.is_ascii_digit c then enclose "{\\isadigit{" "}}" c else c);