Boléro epitomises Ravel's preoccupation with restyling
and reinventing dance movements. It was also one of the
last pieces he composed before illness forced him into
retirement: the two piano concertos and the Don
Quichotte à Dulcinée song cycle were the only
compositions that followed Boléro. Ravel himself has
made two cuts in 1929 for his Bolero piano, one with
two hands and one duet. They are very rarely performed
in public. (Wikipedia)