Tritone substitution: Gb7 can be replaced by C7 (a tritone away). Both chords share the same tritone between the 3rd and 7th, resolving to the same tonic.
The augmented 11th forms a tritone with the root and avoids the close clash that a perfect 11th creates with the 3rd. The combination of major 3rd, minor 7th, and #11 matches the Lydian dominant scale.
Application
Lydian harmony
Jazz and fusion
Film scoring
Voicing & structure
Root position
v1Gb(Gb4)Bass
root
v2Bb(Bb4)M3from Gb
v3Db(Db5)m3from Bb
v4Fb(Fb5)m3from Db
v5Ab(Ab5)M3from Fb
v6C(C6)M3from Ab
Harmony
Compatible scales
All chord tones are contained in these scales — use them for improvisation.