>>> 1. Make a printer filter text into postscript, but leave postscript
>> This is not possible without resorting to human help; PostScript
>> _is_ text

Two people replied,

> If the first two characters are "%!", it's PostScript.

> Hmm, this is fairly easy.  Just get a decent printer filter.  [...]
> PS files always start with !#PS, so you can recognize them quite easy.

Once more: this is a reasonable guess, but only a guess; it is
perfectly valid for text files to start with %!, or PostScript programs
to not start with a comment.  (Requiring PostScript code to start with
a comment is as silly as cc refusing to compile something that doesn't
start with /*.)

As I mentioned and all these respondents who have been pointing at %!
seem to have ignored, I have on occasion wanted to print _exactly the
same file_ twice, once as as PostScript program to be run and once as a
text file to be printed.  _No_ guessing mechanism that looks at only
the contents of the file can possibly suffice.

					der Mouse

			    mouse@collatz.mcrcim.mcgill.edu