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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 _context_names():
 """Return list of valid context names."""

    import inspect

    from renku.models import provenance
    from renku.models._jsonld import JSONLDMixin

    for name in dir(provenance):
        cls = getattr(provenance, name)
        if inspect.isclass(cls) and issubclass(cls, JSONLDMixin):
            yield name