The Micrologus is a treatise on Medieval music written by Guido of Arezzo, dating to approximately 1026.
This treatise outlines singing and teaching practice for Gregorian chant, and has considerable discussion of the composition of polyphonic music.
One point of importance is his guideline for the occursus (meaning "meeting" or "concurrence", running on the same path), which is a predecessor of the later cadence.
An occursus occurs where two voices approach a unison.
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