Pauli asks why in Heisenberg's calculations the force-potentials are always real.

Pauli discusses Heisenberg's formulae in his letter of the 13 September 1957.

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 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 is very optimistic about the results so far. He suggests as a title for the the joint paper: "On the interpretation of isotopic spin". He gives some moreconclusions. He makes some mathematical comments on unitary and pseudo-unitary transformations, and the dichotomy of the vacuum.

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

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.