Song of the Variable Time-Unit, 4/4/2019; or, I Shoulda Learned to Play the Gittern By Roderick on April 5, 2019 0 Angelorum psalat, a 14th or 15th-century work by the mysterious composer “S. Uciredor” (read it backwards), who may or may not be the same person as the 15th-century Spanish musician Rodrigo de la Guitarra: