code: func isValidSeq(names []string) bool {
  	var lastSeq uint64
  	for _, name := range names {
  		curSeq, _, err := parseWalName(name)
  		if err != nil {
  			plog.Panicf("parse correct name should never fail: %v", err)
  		}
  		if lastSeq != 0 && lastSeq != curSeq-1 {
  			return false
  		}
  		lastSeq = curSeq
  	}
  	return true
  }
docs: // names should have been sorted based on sequence number.
  // isValidSeq checks whether seq increases continuously.