I think Google has mistranslated the last sentence, which should begin: "Two other volumes will appear" Unless your French is excellent, I would wait for the proposed translation.This first volume is an introduction suitable for all those new to the Gregorian chant and want to practice. This teaching focuses on four main themes: the text, melody, rhythm and style.
Two other volumes seem to be for the singers and the choir masters wishing to improve in the liturgical practice of Gregorian chant.
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