The letter contains some calculations on irreducible group representations.

Kemmer replies to a letter by Pauli. He writes on calculations on the regular representation of the Abel group and about irreducibility of this representation.

Kemmer rejects an assumption made by Pauli.

Continuation of the letters of 8/9 May.

This reply to Pauli's letter is about the irreducibility of the n- group representation.

Continuation of the letter of 8 May, Kemmer makes more remarks about the relation of his representation of the wave equation to de Boglie's.

This reply to Pauli's letter, concerns the representation of the wave equation with spin.

Kaufman discusses properties of a determinant and invariance of his Lagrangian and he answers a question from Pauli.

Källén writes on his recent attempts to simplify the calculations on quantum electrodynamics.

Källén proves a mathematical identity and he dicusses the properties of a function.