Pauli thanks Källén for the manuscript. He writes about the Tamm-Dancoff method and some known negative attitude towards it. Small changes in the manuscript and the re-writing of the appendix.

Pauli asks for classification of Klein's work.

Pauli has some more suggestions for minor changes in the paper.

Pauli criticizes Klein's notation and a commutator relation. He refers him to Rosenfeld (1930).

Pauli talks about his completely different views from those of Schrödinger on the interpretation, on the difficulties and the tendencies of quantum mechanics. He makes a formulation of a few theses about physical theories. He says that among the physicists opposed to quantum mechanics Einstein is understood best by him.

Heisenberg writes on the application of Pauli's ideas to quantum electrodynamics and on the avoidance of ghosts.

Heisenberg talks about some relations between Lee's theory and his.