The minor 7 flat 5 chord is not just an altered minor 7 chord.
It has it's own unique sound and used in jazz.
Diminished 7
These are two forms of the diminished 7 chord (the small o before
the 7 means diminished) The root of the chord could actually be
any on of the notes, but for simplicity and lack of further explanation,
just think of the lowest note as the root (6th or 5th string)
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Page 2, Dominant 7 and Minor 7 chords