Chant après chant was the only work you wrote to a commission—from the Strasbourg Festival on behalf of the locally formed but already internationally renowned percussion sextet. Founded in 1962, the group had a vigorous commissioning policy—of necessity, since at that point the active repertory for percussion ensemble was rather small, comprising Varèse's Ionisation, Cage's First Construction (in Metal) and a few other pieces. You could have heard the ensemble at any of a number of concerts in 1964–5, including the Domaine Musical evening for which you had once been writing your Concerto (13 May 1964) as well as the first Paris performance of Messiaen's Couleurs de la Cité Céleste (16 December 1964) and the world première of his Et exspecto resurrectionem mortuorum for symphonic wind and percussion (in the Sainte Chapelle, 7 May 1965). Alternatively, they might have approached you on the basis of your percussion writing in Séquence and …au delà du hasard. However the contact came about, it was definitely made by November 1965, the month when you entered Chant après chant into your Mort de Virgile scheme, and when Jean Batigne, from the ensemble, sent a list of their instruments.

Other information you gained from scores. Someone transcribed for you the instrumentation of Maurice Ohana's Etudes chorégraphiques, which the Strasbourg team had introduced in 1963. You also studied Berio's Circles for voice, harp and two percussionists (1960), and you might have acquired for the same purpose copies of Boulez's Improvisation sur Mallarmé I for voice and percussion ensemble (1957) and his Eclat for percussion nonet and six other instrumentalists (1965).