code: def projection(self, exprs):
          
          w = self._get_window()
          windowed_exprs = []
          exprs = self.table._resolve(exprs)
          for expr in exprs:
              expr = L.windowize_function(expr, w=w)
              windowed_exprs.append(expr)
          return self.table.projection(windowed_exprs)
docs: Like mutate, but do not include existing table columns