  In time reversal symmetric systems with half integral spins (or more
concretely, systems with an antiunitary symmetry that squares to -1 and
commutes with the Hamiltonian) the transmission eigenvalues of the scattering
matrix come in pairs. We present a proof of this fact that is valid both for
even and odd number of modes and relies solely on the antisymmetry of the
scattering matrix imposed by time reversal symmetry.
