def get_pairs(lines):
    """Returns list of pairing indices.
    
        - Changes indices to zero based rather than 1 based.
    """
    pairs = []
    for l in lines:
        if l.startswith('] def'):
            break
        elif l.startswith('['):
            first,second = l.strip('\n[]').split()
            pairs.append([int(first)-1,int(second)-1])
    return pairs