message: added mod_neg
diff: @@ -70,6 +70,10 @@ impl GroupOrderElement {
  unimplemented!();
  }
  + pub fn mod_neg(&self) -> Result<GroupOrderElement, CryptoError> {
  + unimplemented!();
  + }
  +
  pub fn to_string(&self) -> Result<String, CryptoError> {
  unimplemented!();
  }
  