End to end, the five Beethoven cello sonatas run about two and a half hours. By contemporary programming standards, that makes for let’s say a half-marathon, yet strange to say, complete live performances are virtually unheard of. That’s hardly the case with the composer’s five piano concertos, which are scheduled as a set all the time, though seldom in a single day. Cycles of his 9 symphonies, his 10 violin sonatas, his 16 string quartets, and 32 piano sonatas are likewise fixtures of the concert repertoire. The cello sonatas, as you might guess, are top-notch, and this opportunity to hear them en bloc is most welcome. In an inspiring show of collegiality that also raises the competitive stakes, the five works are being divvied up among the Seattle Symphony’s cellists. What about the piano parts, we wonder? —M.G.