Marten Jansson Missa brevis E flat minor. The “Missa brevis in E flat minor” for mixed choir a cappella has been composed in the tradition of the short Mass (without Credo) and can be easily managed by most choirs. Thanks to its conciseness, it is suitable for use in church services, while its delightful harmonic layout and consciously simple melodies (with clear allusions to folk music) also make it perfect for concert performance.