Alan and Matt,

This is too much of a coincidence to be true! MY favorite chord is C13b9#9#11b13 but, to prove the point, I see it in Alan's formulation as Chord X /Chord Y where X = Ab (major triad) and Y = Gbm7, i.e., Ab/Gbm7.

Let's check it on the piano. With the left hand play the inversion Db E Gb A for the slash chord Gbm7 and the inversion C Eb Ab in the right. Actually, you can use any inversions you like.

Listen to that killer chord. No wonder it's a fave.

Reading from left to right, we have Db E Gb A C Eb Ab, which in the key of C works out to

b9 3 #11 13 ROOT #9 b13.

The fifth and dominant seventh are suppressed. The bassist can play any of these notes, but C, Gb and Ab seem like preferred choices.

Aleck