...fascinating guy to just sit around and listen to--he had a million stories for every subject, and they never got old. I got to know him at The University of Chicago when he was a visiting prof in the music department and I was a grad student. Nearly got him killed in about 1983 near Ojai, driving him and two friends through the canyons so he could try to spot some condors. He survived until yesterday when cancer got him at age 85. A New York Times obit is linked below.
Here is a 1960s performance of one of his encore pieces, a typical late 19th-early 20th-century style quasi-improvisational arrangement of the scherzo from Mendelssohn's music for "A Midsummer Night's Dream." I heard him play this back in 1980 in the Boston apartment of his partner, Henri Zerner, right before he ruefully informed my friend and I that they only had two lobsters--and that there was thus not enough for us to stay for dinner.
Here is a much later Rosen--late 90s, in a conversation with his very long-time friend, Elliott Carter (who just died last month, barely short of his 104th birthday). The pic shows them in Carter's apartment in NYC.