Music with three staves

[deepblue]

Hi, I would very much appreciate some help with this particular portion of Philip Glass Etude 5. There are three staves, two treble and one bass. I have seen three staves in other works, but I cannot seem to get what is happening beginning in section 18. Thank you.

[quantum]

It's a way of clearly separating voices so a single staff doesn't get crowded with notes.  Both hands share the responsibility of playing the middle staff, with the hand that is free taking up the task.  If there are held notes, use the pedal to aid in sustain of the harmony. 

So for example, starting at section 18 your middle staff hand assignments would be:
R | R L L | R | R ...

or alternatively taking the chord Ab, Bb, E, Ab with the right hand alone.

R | R R L | R | R ...