As promised I upload Kenneth Levy's contribution to Ladislav Mokrý's conference “Anfänge der slavischen Musik” at Bratislava in August 1964 which was published in exactly the same year like Constantin Floros' publication dedicated to the same notation:
Levy, K., 1966. Die slavische Kondakarien-Notation. In L. Mokrý, ed. Anfänge der slavischen Musik. Konferenz “Anfänge der slavischen Musik” August 1964. Bratislava: Verlag der Slowakischen Akademie der Wissenschaften, 77–92.
For a better understanding (and more contemporary references by Floros and Levy) I recommend Miloš Velimirović' summary (see also Floros’ review of Levy “The Slavic Kontakia and their Byzantine Originals” 1964 here):
Velimirović, M., 1972. The Present Status of Research in Slavic Chant. Acta Musicologica, 44(2), 235–265. doi:10.2307/932170.
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