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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 resolve_sid(sid):
 """Get the PID to which the ``sid`` currently maps. Preconditions: - ``sid`` is verified to exist. E.g., with d1_gmn.app.views.asserts.is_sid(). """

    return d1_gmn.app.models.Chain.objects.get(sid__did=sid).head_pid.did