Leifs, Jón (1899-1968). Baldr, Opus 34 [textless opera (the first according to Guinness Book of Music, 2nd ed, 1981, p. 156, but also described as "a tone poem for orchestra", composed 1950; composer's name spelled "Liefs" and title spelled Baldur in some sources]
Leifs, Jón. Loftr [textless opera according to Baker's Biographical Dictionary, 7th edition, p. 1333, first performed 1938]