Correspondence; LS-Dimitri Mitropoulos; LS-Bruno Walter; Programming; Repertoire; Soloists; Changes in Programs; 1947 Spring Tour programs and rehearsal; Failed attempt at American broadcast premiere of Mahler: Symphony No. 6; Premiere of new symphony by Ernst Krenek, and request from Dimitri Mitropoulos of fee to composer; Telegram from Dimitri Mitropoulos to Jean Sibelius; Soloist issues for 1947 concerts conducted by Dimitri Mitropoulos, relating to resignation of Artur Rodzinski; Suggestions from Dimitri Mitropoulos and Leopold Stokowski regarding changes in orchestra personnel