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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 pl2nvc(plane):
 """ Return a unit normal vector and constant that define a specified plane. http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/pl2nvc_c.html :param plane: A SPICE plane. :type plane: supporttypes.Plane :return: A normal vector and constant defining the geometric plane represented by plane. :rtype: tuple """

    assert (isinstance(plane, stypes.Plane))
    normal = stypes.emptyDoubleVector(3)
    constant = ctypes.c_double()
    libspice.pl2nvc_c(ctypes.byref(plane), normal, ctypes.byref(constant))
    return stypes.cVectorToPython(normal), constant.value