While the sprinkling is being done, an antiphon or a hymn is sung. The priest, with his assistants, says the psalm "De profundis" with the antiphon "Si iniquitates". In the Gregorian system, psalm tones are based on the mode of the antiphon. This evidently means twelve psalms, two under each antiphon. Then follows the proper "Antiphon of the Mysteries" (Unitha d' razi), answering to the offertory. In every Nocturn the three psalms are said under one antiphon. Parce Domine is a Roman Catholic antiphon (a short chant in Christian ritual). Compline, as revised in 1969 after the Second Vatican Council, ends with the antiphon alone. Mozart composed an antiphon "Veni Sancte Spiritus" in 1768. Then follows a variable antiphon of thanksgiving, a post-communion, and a dismissal. Barnes's verse play "The Antiphon" (1958) is set in England in 1939. The Marian antiphon is said in the low voice. Continuing theological discussions exist as to the origin and exact timing of this Marian antiphon. On reaching the church the antiphon "Exsultabunt" is repeated. Others include Gorgias, Prodicus, Hippias, Thrasymachus, Lycophron, Callicles, Antiphon, and Cratylus.