The late Morton Feldman once said that composers make plans and music laughs. Feldman should know. He was an extraordinary, pioneering composer who made an impressive and unique contribution to 20th-century American music. He also was Edgar Varese Professor of Composition at the University at Buffalo from 1972 until his death in 1987. This year marks his 80th birthday and in celebration, the UB Music Library has opened an exhibition of material from its Morton Feldman Collection that will run through Sept. 11.