Degenerate modes (the parenthesis in the title reports the corresponding eigenvalue divided by the largest eigenvalue). The degenerate mode of the temperature (left) map reconstruction is the global offset. The Q and U maps on the right are one of the two singular modes of polarization, the other mode is very similar: Q and U maps are swapped and the sign of one of them is flipped. The degenerate modes of the polarization are more complex because of the modulation of the polarization angle during the observation (see Sect. 4.2). For the same reason the degeneracy of these modes is partially broken (though they have to be treated as singular in order to preserve the numerical stability of the inversion of the matrix).