This section, measures 19-20 of the third movement, is extremely difficult, and the right hand's progression in thirds cannot be played without considerable technique. Therefore, I will explain one method to manage playing it.

On the second beat of measure 19, the right hand plays the first two thirds (A-F#, G-E), and from the next F#, plays single notes: F#, E, D. At the F#, the left hand plays the inner voices of the right hand: D and C#. Then, on the first beat of measure 20, it descends with B, A, G, F#, E.

Similarly, on the second beat of measure 20, the right hand plays the thirds B-G, A-F#. From there, it plays single notes G and F#, and then enters measure 21, playing E, F#, G, F#, E. The left hand, on the second beat of measure 20, plays E and D, which are the lower notes of the third third. It also plays the right hand's inner voices in measure 21 (C#, D, E, D, C#) with the left hand, along with the four A's below them.

Measures 77-78 are similar.

As indicated in the score, playing all the thirds with the right hand at the fast tempo of Vivace assai is extremely difficult. Please try various contrivances by utilizing the left hand.