static File pathToJavaxJar() ctex {
  int x = latestInstalledJavaX();
  File xfile = new File(userHome(), ".javax/x" + Math.max(x, 30) + ".jar");
  if (!xfile.isFile()) {
    print("Saving " + f2s(xfile));
    String url = "http://tinybrain.de/x30.jar";
    byte[] data = loadBinaryPage(url);
    if (data.length < 1000000)
      fail("Could not load " + url);
    saveBinaryFile(xfile.getPath(), data);
  }
  ret xfile;
}