public static boolean checkExpon(BigInteger x){
  return !(x.compareTo(BigInteger.ONE) > 0 && x.compareTo(SM.ORDER_S) <= 0);
}

public static boolean checkExpon ( BigInteger x ) { return ! ( x . compareTo ( BigInteger . ONE ) > 0 && x . compareTo ( SM . ORDER_S ) <= 0 ) ; }
check that an biginteger is in the right range to be a ( non - zero ) exponent
