I vividly remember three songs sung from the stage. One was "Blowin' in the Wind," performed by Peter, Paul and Mary. I had first heard the song sung by Dylan, and, in my teenage foolishness, still resented them for leaving out his "yes'ns" before each line. Their performance was stirring, nonetheless.   I was thrilled that Bob himself was there, singing "Only a Pawn in Their Game," about Medgar Evers. And of course, ending with "We Shall Overcome," which I think we all recognized as the experience of a lifetime. The song was so deeply imprinted in my brain that, on the return bus, I could hear it as if I were wearing headphones, though I did not at the time know what headphones were. I sat there listening to the song, sung by some quarter million people in my head, just following along.