FA-81048 / Music interval and transposition theory / Member archive
Pitch-class set prime form (right-packed): less packed candidate preferred · case 03
The major triad [0,4,7] keeps the prime form [0,4,7] instead of [0,3,7]: the less packed of the two candidates wins.
Case contract
Input a list of integers. Compute the right-packed normal form of the set and of its inversion (p -> -p mod 12), transpose each to start on 0, and return whichever is more packed: compare the last value, then the penultimate, and so on toward the second (the original wins ties). Empty input returns []; non-integers return None.
Why this case matters
Set-class labelling depends on prime forms being computed identically for every member of a class.
One recorded failure
Sample boundary fixtureThis sample comes from the broken implementation of a controlled reproducer.
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| oracle 0 | [0, 4, 7] | [0, 3, 7] | Failed |
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