fun f (l) {
  infix "===" at "==" (a, b) {
     a == b
  }

  case l of
    {}         ->  1
  | {_}        ->  1
  | a : b : tl ->  a === b && f (b : tl)
  esac
}

local x = read ();

write (f ({}));
write (f ({1}));
write (f ({1, 1}));
write (f ({1, 1, 1}));
write (f ({1, 2, 1}))