Before beginning his solo exploration of Schubert’s piano sonatas later in the same month, Daniel Barenboim is joined by longtime collaborator Radu Lupu for a program of three of the composer’s works for piano duet, with the great F-minor Fantasy, written in Schubert’s last year just before the three final piano sonatas, as the centerpiece. The concert is bookended by the earlier Sonata D 617, one of the works that launched Schubert’s interest in the piano duet medium, and the Divertissement sur des motifs originaux français, a three-movement fantasy much more substantial than its playful title suggests.