 Bloch corresponded with several
mathematicians, including Georges Valiron, George Pólya, Jacques Hadamard and others, giving his return address as only "57 Grande rue, Saint-Maurice", never mentioning that this was a psychiatric hospital.Several of his correspondents were thus unaware of his situation.During the German occupation of France, Bloch (who was Jewish) wrote under aliases, in order to avoid advertising his presence to Nazi occupiers.