Ehrenfest had published a paper 'Some queries concerning the foundations of quantum mechanics'. The file contains a letter from Peierls giving his views as to the answers, a reply from Ehrenfest asking that some of the answers be expanded and suggesting that Peierls publish his views. A further letter from Peierls discussed the points Ehrenfest had raised. He did not publish anything on this because he found that Pauli had published a reply to Ehrenfest which largely overlapped with his own ideas.