code: func (c Chain) Use(i, j int) bool {
  	for _, less := range c {
  		if less == nil {
  			continue
  		}
  		if less(i, j) {
  			return true
  		} else if less(j, i) {
  			return false
  		}
  	}
  	return false
  }
docs: // Use is a sort-compatible LessFn that actually executes the full chain of
  // comparisons.