procedure main(arglist)
   file := open(arglist[1],"r") | &input
   every write(rot13(|read(file)))
end

procedure rot13(s)   #: returns rot13(string)
static a,n
initial {
   a := &lcase || &ucase
   (&lcase || &lcase) ? n := ( move(13), move(*&lcase) )
   (&ucase || &ucase) ? n ||:= ( move(13), move(*&ucase) )
   }
return map(s,a,n)
end