||Snow 2007: "Pope first demonstrates the asymmetry typical of the musical and metrical lines of the "vuelta" in XV- and XVI-century villancicos. Thus armed, she provides a historical excursus that leads back to Galician-Portuguese practices in the CSM (pp. 208-214). With well over 100 examples of the asymmetry in the basic pattern found in the CSM (= a a / b b b a), i. e. in which the third 'b' line of the mudanza repeats the music of the introductory refrain and not the music of the preceding 'b' lines, Pope goes on to weaken further the Arabist theories of Ribera and his followers — in which a perfect symmetry for music and metrical scheme is assumed. Another interesting point made is that the CSM were doubtless designed for solo performance with musical accompaniment (in cases where express repetition of the refrain is not indicated), marking an early decline in responsorial performance patterns (the more normal state of affairs by the time of the fifteenth-century cancioneros."