Moving back to application, I explain here how the four dominants that we made from the diminished create four "altered dominant" sounds. Specifically:

Bb7 -> C = G7b9#9 -> C

Db7 -> C = G7b9#11 -> C

E7 -> C = G13b9 -> C

and of course

G7 -> C = G7 -> C

So, instead of thinking of four varieties of altered "G7" chords, we are thinking of approaching the destination from four different angles. Could be North, South, East and West, or something like that. Could also think where the roots are - approaching from the 5th (normal), from the b7th (backdoor), from the tritone (tritone sub), or from the major 3rd above (13b9).

Soon we will expand these four dominants in a whole world of symmetry