I N T R O D U C T I O N T O V O L U M E 1 6 l x x i x Four years earlier, Blumenthal had asked Einstein to spearhead an effort to re- cruit French authors for a special issue of Mathematische Annalen celebrating the centenary of Bernhard Riemann’s birth (Vol. 14, Docs. 395, 397). Through Paul Langevin, Einstein obtained positive responses from Paul Painlevé, Émile Borel, and Jacques Hadamard (Vol. 14, Doc. 420). In the meantime, Brouwer initiated a protest action against extending an invitation to Painlevé, the former minister of war whom Einstein knew to be an advocate of rapprochement. Citing inflammatory passages from a speech Painlevé had delivered in 1918 to the French Academy, Brouwer stirred up resistance within the board, thereby forcing Hilbert to retreat from his original plan.[60] Invitations would not be sent, but Hilbert authorized Einstein to signal that contributions from French authors were nevertheless wel- come (Vol. 14, Doc. 437). When the special issue finally appeared in 1927, it con- tained no papers by French mathematicians. Nevertheless, it did contain a significant contribution from Einstein’s pen, namely, Einstein 1927a (Vol. 15, Doc. 158). Drawing on George Rainich’s decomposition of the Riemann tensor, Einstein was able to derive the modified field equations he had first introduced in 1919 (Vol. 7, Doc. 17), where he replaced the usual Einstein tensor with its trace- free counterpart. By the mid-1920s, opposition was mounting to the CIR’s boycott policy,[61] and in 1928 Italian mathematicians prepared to challenge the boycott at the forthcom- ing International Congress in Bologna. Brouwer and his closest ally, Berlin’s Ludwig Bieberbach, refused to go along. Instead, they mounted a counter-boycott movement within the German mathematical community, a maneuver that enraged Hilbert. Although weakened by pernicious anemia, the Göttingen mathematician led a large contingent of Germans to the Bologna Congress, thereby ending the pol- itics of exclusion at international congresses. For an address that he planned, but probably never delivered, he wrote, “mathematics knows no races… for mathemat- ics, the whole cultural world is a single country.”[62] In the immediate wake of these events, Hilbert decided that the moment was ripe to remove Brouwer from the editorial board of Mathematische Annalen. With his message from 15 October 1928 (Doc. 282) he sought authorization to do so from the three other principal ed- itors, Einstein, Blumenthal, and Carathéodory, who had since assumed Klein’s former position. Carathéodory felt deeply troubled by Hilbert’s unilateral decision and shared these misgivings with Einstein (Abs. 694, 704). After his efforts to mediate failed completely, Carathéodory realized that Brouwer would never yield and was pre- pared to fight to the end. In a subsequent plea to the full board, Brouwer took the opportunity of stating his position, which he claimed accorded with conclusions he and Carathéodory had reached during a private meeting that took place in Laren on