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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 phi_s(spin1x, spin1y, spin2x, spin2y):
 """ Returns the sum of the in-plane perpendicular spins."""

    phi1 = phi_from_spinx_spiny(spin1x, spin1y)
    phi2 = phi_from_spinx_spiny(spin2x, spin2y)
    return (phi1 + phi2) % (2 * numpy.pi)