Canonical structural spine
The work's own structure
Reviewed edition: Ambrose. Sanctii Ambrosii Opera, Pars Quarta (CSEL 32.4). Karl Schenkl, editor. Prague; Vienna; Leipzig: F. Tempsky; G. Freytag, 1902. Division axes: book → section. Structural nodes alone do not assert commentary citations.
Record-local commentary evidence
Commentary citations: work locus ↔ Dante locus
These citations occur in later commentary. They do not, by themselves, mean Dante cited this work.