PROCEDURE kuerzen(VAR res:bruch);
VAR a,b,h:longint;
BEGIN
  a:= abs(res.zaehler); b:= abs(res.nenner) ;
  REPEAT
    IF a<b THEN
    BEGIN
      h:= a; a:= b; b:= h
    END
    ELSE a:= a MOD b;
  UNTIL b = 0;
  IF res.nenner < 0 THEN a:=-a;
  res.zaehler:= res.zaehler DIV a;
  res.nenner:= res.nenner DIV a
END;