Pauli writes of his going to the conference in Pisa where he will discuss Källén's letter. He talks about Landau's papers whose general gist is like that of Källén's and about his doctoral student Enz and his work.

Pauli talks about offprints of their common paper.

Pauli asks him to send a copy of his work to Heisenberg. He mentions an error found in Heisenberg's paper.

Pauli talks about a manuscript sent by Heisenberg and a question whether unitarity of S-matrix, commutativity of field-operators and regularity of commutators on the light-cone can be fulfilled in the case of abandoning a positive-definite metric. He writes about Wightman's axioms and their inapplicability to physics.

Pauli suggests a note correcting the results of Nishijima. He questions whether Heisenberg's description of physical scattering processes in the Lee model comes to grief through discrete states of negative norm or of complex energy He also asks whether "Heisenberg-models" can be constructed for which the unitarity of the S-matrix is preserved in an indefinite metric of the field-operators?

Pauli talks about Schwinger's contribution to the Handbuch.

Pauli talks about the still existing difficulties with the Handbuch-article and Springer. He writes of his lecture on many-particles-systems. He does not want to touch field quantization for a while.

Pauli doubts some of Källén's formulae for the Lee model. He writes about calculations of convergence of integrals and about the proof for the consistency of Peierl's method.