Musical illustrations of Arvo Pärt’s Spiegel im Spiegel and Beatitudes are now published in Arvo Pärt’s Resonant Texts: Choral and Organ Music 1956–2015 (Shenton 2018) and Illiano, R., & Locanto, M. (Eds.). (2019). Twentieth-century music and mathematics. Brepols.
These unpack the musical mechanisms of Arvo Pärt’s music as outlined in this lecture below.