def _sortArrayLessThan(data, elementSize, a, b):
    """Return True iff element a is less than element b.
    
    Each element consists of 'elementSize' array indices.
    """
    # Pull out index 0 just for speed.
    if data[a * elementSize] < data[b * elementSize]:
        return True
    if data[a * elementSize] > data[b * elementSize]:
        return False
    for i in range(1, elementSize):
        if data[a * elementSize + i] < data[b * elementSize + i]:
            return True
        if data[a * elementSize + i] > data[b * elementSize + i]:
            return False
    # Here: a == b
    return False