code: func simpleHashFromHashes(hashes [][]byte) []byte {
  	// Recursive impl.
  	switch len(hashes) {
  	case 0:
  		return nil
  	case 1:
  		return hashes[0]
  	default:
  		left := simpleHashFromHashes(hashes[:(len(hashes)+1)/2])
  		right := simpleHashFromHashes(hashes[(len(hashes)+1)/2:])
  		return SimpleHashFromTwoHashes(left, right)
  	}
  }
docs: //----------------------------------------------------------------
  // Expects hashes!