zero sum (zerosumm)

Whose woods these are I think I know. His house is in the village though; he will not see me stopping here to watch his woods fill up with snow. My little horse must think it queer to stop without a farmhouse near between the woods and frozen lake the darkest evening of the year. He gives his harness bells a shake to ask if there is some mistake. The only other sound's the sweep of easy wind and downy flake. The woods are lovely, dark and deep, but I have promises to keep, and miles to go before I sleep, and miles to go before I sleep.