def _look_ahead (index_sentence,context, maximum) :
    """Generate the look ahead context starting with the sentence index and looking no more
    than max number of sentences"""

    context_pairs = []
    for i in range(1, context+1):
        s_index = index_sentence+i
        if s_index<=maximum:
            context_pairs.append((index_sentence, s_index))
    return context_pairs