Chopin & Liszt arranged by Saint-Saëns
Given the 'romantic' nature of these two sonatas, Saint-Saëns could have been forgiven for producing two-piano versions that treated the originals as bases for his own imaginings. In fact, as far as a fourth party can judge, he has been scrupulous in respecting the composers' intentions.
LisztSonata in B minor
ChopinSonata No. 2 in B♭ minor, Op. 35 (arr. Saint-Saëns)