Watch the Common Tones online guitar lesson by Brad Carlton from Chord Studies: Jazz Turnarounds Vol. 2
This example pertains to a I-vi-ii-V progression in the key of F, with two principles: For the I chord we're substituting the III chord, that's where the Amin7 comes from. We can do this because of the common tone principle; any chords that are a third apart either higher or lower share common tones. The vi chord in this progression would be the D7#9, but we apply the flat-five substitution in the base, giving us a chromatic descending bass line. The ii chord is a Gmin7, and our V chord would have been C7#9, but we're applying the flat-five substitution there as well.