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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 spin_in_system(incl, long_an):
 """ Spin in the plane of sky of a star given its inclination and "long_an" incl - inclination of the star in the plane of sky long_an - longitude of ascending node (equator) of the star in the plane of sky Return: spin - in plane of sky """

    #print "*** spin_in_system", incl, long_an, np.dot(Rz(long_an), np.dot(Rx(-incl), np.array([0,0,1])))
    # Rz(long_an) Rx(incl) [0, 0, 1]
    return np.dot(Rz(long_an), np.dot(Rx(-incl), np.array([0.,0.,1.])))