static Pair<L<File>> addMegaLibrary(ClassLoader cl, S snippetID) {
  var jars = allJarFiles(unpackZipLibrary(snippetID));
  new L<File> added;
  new L<File> alreadyThere;
  for (jar : jars)
    (addByteCodePathToClassLoader(cl, jar) ? added : alreadyThere).add(jar);
  ret pair(added, alreadyThere);
}