[Fenfire-dev] Pointer obsoleting

[Tuomas Lukka]

Was discussing with Benja on irc the pointer obsoleting problem.

To formalize the problem, it is this:

        on each computer, there is some set of pointers P
        between the pointers, there is the transitive
        "obsoletes" relation.

        On the computer, a new block can be made that 
        obsoletes some of the blocks on that computer.

        Blocks are exchanged between computers and can vanish
        from the network.

        A block may reappear from a back-up tape at any time.

The problem is, given the blocks *currently accessible*,
to show that one of the currently accessible blocks indeed obsoletes
the block restored from the backup.

Now, it's easy to show that if everyone conspires against you,
you *need* to always store *all* obsoleted blocks in each pointer,
or a pointer that *you* explicitly save.

        Tuomas