code: func symSearch(u, w Comparators) int {
  	start, stop, p := 0, len(u), len(w)-1
  	for start < stop {
  		mid := (start + stop) / 2
  		if u[mid].Compare(w[p-mid]) <= 0 {
  			start = mid + 1
  		} else {
  			stop = mid
  		}
  	}
  
  	return start
  }
docs: // symSearch is like symBinarySearch but operates
  // on two sorted lists instead of a sorted list and an index.
  // It's duplication of code but you buy performance.