||Manuscript, n.d.[12th century].
||Choirbook, E-SC s.s.
The DIAMM link above cites RISM: "All the part-music is à 2 except no. 4, which has often been considered the earliest three-part composition. Wagner (see below), 166, considered the highest part to be an expansion of or substitute for the middle one, and certainly there seems to be some justification for this suspicion."