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Martin Heidegger, Heinrich Rickert (2002) Briefe 1912 bis 1933: und andere Dokumente (edited by Denker Alfred), Frankfurt am Main, Klostermann.
Brief von Husserl an Ingarden, vom 5.4.1918
Edmund Husserl
pp. 7-10
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(1968) "Edmund Husserls Briefe an Roman Ingarden", in: Husserl Edmund, Briefe an Ingarden, Den Haag, Nijhoff, pp.1-105.