code: def highlightSubsequence(sequence, x1, x2, start=' [', stop = '] ') :
  	
  
  	seq = list(sequence)
  	print x1, x2-1, len(seq)
  	seq[x1] = start + seq[x1]
  	seq[x2-1] = seq[x2-1] + stop
  	return ''.join(seq)
docs: returns a sequence where the subsequence in [x1, x2[ is placed 
  	in bewteen 'start' and 'stop