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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def bootstrap_jar_classfiles(self):
 """Returns a set of classfiles from the JVM bootstrap jars."""

    bootstrap_jar_classfiles = set()
    for jar_file in self._find_all_bootstrap_jars():
      for cls in self._jar_classfiles(jar_file):
        bootstrap_jar_classfiles.add(cls)
    return bootstrap_jar_classfiles