9947 / 18210 · Workshop 82 — Symmetrical Harmony and Harmonic Geometry: Diminished Cycles, Augmented Triads, Whole-Tone Motion, Major-Third Systems, and Escaping Ordinary Tonal Gravity← prev⊞ allnext →
82.40Level 19 — dominant ♭9 connection
G7♭9:
G-B-D-F-A♭.
Remove root G.
Remaining:
B-D-F-A♭.
That's:
B°7.
Therefore:
a dominant ♭9 contains a diminished seventh chord built on its 3rd.
You already know this.
Now symmetry explains why it is so flexible.