@libraz/libcantus - v1.1.0
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    Type Alias Alteration

    One altered degree: which one, and by how much.

    alter: 0 is not redundant — it says the degree is present and unaltered, which is what the natural ninth of a thirteenth chord is.

    type Alteration = {
        degree: AlteredDegree;
        alter: -1 | 0 | 1;
    }
    Index
    alter: -1 | 0 | 1