Printing rational numbers as such is certainly correct, but not really
helpful most of the time; the user can still see the correct rational
by printing the stack ("p").

 * SBCL does not have command line arguments in *ARGS* (and is
   hesitant to reveal where or if at all), so this variable is
   grounded just in case; this means with SBCL we cannot call the
   program with command line args like "$ luc 3 4 +", but that is
   bearable
 * flush output after prompt; this should have been done in the
   first place anyway
 * to be independent on the precise version of Lisp called, move
   the system dependency to some "lisp", which must be in the PATH

Conflicts:
	luc.lisp

print it as a float (and not change it)

overflow for biggish results)

Conflicts:
	luc.lisp

manually resolved conflict between a partly begun and the finally implemented {...} bracketing

n2 n3 'func }, e. g. { 1 2 3 4 5 6 7 '* } => 5040