“1. One day in early September 1966, the poet Robert Duncan, then 47, was walking to a streetcar stop in San Francisco when lines of verse began drifting to him out of nowhere. He held onto the phrases until he could scribble them down at the stop. The rest of what would become two poems—’Passages’ 28 and 29—occurred ‘in rushes on the streetcar and on the Berkeley bus, me muttering ecstatically. All there by the time I reacht Berkeley.’  These poems would appear toward the end of what may be Duncan’s finest book, Bending the Bow (1968), which was written largely in response to the Vietnam War. He laid out their impetus in a letter to one of his dearest friends, Denise Levertov: he had been dwelling on Victor Hugo’s visionary poem in which the angel Liberty is born from a single feather falling from Satan’s wings as…