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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 is_installed():
 # type: () -> bool """ Returns whether the C extension is installed correctly. """

  try:
    # noinspection PyUnresolvedReferences
    from ccurl import Curl as CCurl
  except ImportError:
    return False
  else:
    # noinspection PyUnresolvedReferences
    from iota.crypto import Curl
    return issubclass(Curl, CCurl)