Pauli dicusses the alternative dipole ghosts or complex roots. He writes on difficulties in the case of Lorentz-invariant interactions. The Tamm-Dancoff approximations are not sufficient in this case.

Pauli writes about the isotopic-spin problem.

Pauli continues his last letter of the 13 December.

Pauli talks about the problem of mathematical formulation of symmetry-violations in the case of the dichotomy connected with the interpretation of dipole ghosts and complex ghosts. He hopes for progress in the question of leptons. There is a more positive attitude on the question of indefinite metric.

Pauli talks more about Springer and time-dependent wave-packets in a Lee model with complex roots. He writes on the interpretation of isotopic spin.

Pauli writes on further calculations about the physics of elementary particles, and about more group theoretical considerations. Possibly there exists complementary between the space-time description in the micro-world and the physical probability.

Pauli explains what he means by "antisymmetric metric". Hereby one gets the masses of leptons different from zero.

Pauli writes about his impending trip to the USA. He writes about his work with Heisenberg.

Pauli is glad about Heisenberg's impending visit. He writes a few words about the next stage of the discussion, especially the eigenvalue problem for rest masses.

Pauli replies to Källén's solution in his letter of the 9 January 1958 with additional remarks about $\lambda_{o}$-particles, the identity of "isospace" with Hilbert-space and the fourfold degeneracy of the vacuum and its removal.