def move_ops(instructions, relative_path=''):
    """ensure move operation from package/unpackage instructions are unique.
    Consider that move operations are considered equal if they share the source. That is you can't pack
    the same file into two different places neighter you can unpack the same file in multiple places.
    A move operation from successive instruction in the list will overrid any previous one.
    """
    ops = set()
    for i in instructions:
        ops = ops.difference(i.file_op())
        ops = ops.union(i.file_op())
    return ops
