Neapolitan Sixth Chord Theory Things   William Wieland
N6 = FlatII6   The Neapolitan Sixth Chord is a predominant.
  c: i  iv  V7 i 
  c: i  N6 V7 i 
An example of a Neapolitan sixth chord appears
near the end of this simple piano transcription:
Gounod Funeral March of a Marionette
(only 1 or 2 chords per measure).

Another clever example:
Chopin C minor Prelude, op. 28, no. 20.
Voice Leading:
do - ra - ti - do     (m2 - d3 - m2)
sol - le - sol - sol     ( step)
me - fa - fa - me     (whole step)
Bass:do - fa - sol - do     (1 - 4 - 5 - 1)