D O C U M E N T 5 0 5 A P R I L 1 9 2 9 7 1 1 ALS. [143 224]. [1] Location determined by the fact that he is staying with the Lebachs. Date determined by refer- ence to his expected return to Berlin on 25 April 1929 (see Doc. 507). [2] Einstein had arrived in Düsseldorf around 17 April (see Abs. 1121). [3] On the purchase of land for the summer house, see Doc. 468. [4] Willy Lebach and Grete Lebach-Bachwitz. [5] Cornel Lanczos. [6] Lanczos and Einstein appear to have found their collaboration frustrating. For a discussion, including Lanczos’s recollections as reported later to Carl Seelig, see Havas 1989, pp. 249–250, and Doc. 366 for a sample of their debate over the problem of motion during which Lanczos contributed some critiques of Einstein’s work. [7] The relevant business may have been Elemente- und Apparatebau Carl Lebach (see Adreßbuch Berlin 1930, p. 16664). [8] Hans Albert Einstein was living in Dortmund. [9] She was possibly named Genia (see Doc. 507). [10] On the illnesses of Ilse Kayser-Einstein, see Doc. 224. [11] Elsa and Margot Einstein and Ilse Kayser-Einstein. [12] Possibly a poem by Emil Schröder (1896–1977), a German editor and author (see [48 419]).