In the gutter, a poem called ''Snow'' where the real thing was three months ago; a ripped-out page - to keep . . . let go - you can read if you will while the wind is slow The light turns green as the world turns; Go, this is no time to read about snow; nor is this the place. Let the wind blow. The Sweeper will come to sweep up ''Snow.'' When has a poem made the traffic slow? The real thing was not ''Snow,'' but snow.