def _move_delta_lbound(d, bytes):
    """Move the delta by the given amount of bytes, reducing its size so that its
    right bound stays static
    :param bytes: amount of bytes to move, must be smaller than delta size
    :return: d"""
    if bytes == 0:
        return
    d.to += bytes
    d.so += bytes
    d.ts -= bytes
    if d.data is not None:
        d.data = d.data[bytes:]
    return d
