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## Possible Types of Gödel Machine Self-Improvements

Which provably useful self-modifications are possible? There are few limits to what a Gödel machine might do.

1. In one of the simplest cases it might leave its basic proof searcher intact and just change the ratio of time-sharing between the proof searching subroutine and the subpolicy --those parts of responsible for interaction with the environment.

2. Or the Gödel machine might modify only. For example, the initial may be a program that regularly stores limited memories of past events somewhere in ; this might allow to derive that it would be useful to modify such that will conduct certain experiments to increase the knowledge about the environment, and use the resulting information to increase reward intake. In this sense the Gödel machine embodies a principled way of dealing with the exploration vs exploitation problem [20]. Note that the expected utility (equation (1)) of conducting some experiment may exceed the one of not conducting it, even when the experimental outcome later suggests to keep acting in line with the previous .

3. The Gödel machine might also modify its very axioms to speed things up. For example, it might find a proof that the original axioms should be replaced or augmented by theorems derivable from the original axioms.

4. The Gödel machine might even change its own utility function and target theorem, but can do so only if their new values are provably better according to the old ones.

5. In many cases we do not expect the Gödel machine to replace its proof searcher by code that completely abandons the search for proofs. Instead we expect that only certain subroutines of the proof searcher will be sped up--compare the example in Section 4.4--or that perhaps just the order of generated proofs will be modified in problem-specific fashion. This could be done by modifying the probability distribution on the proof techniques of the initial bias-optimal proof searcher from Section 5.

6. Generally speaking, the utility of limited rewrites may often be easier to prove than the one of total rewrites. For example, suppose it is 8.00pm and our Gödel machine-controlled agent's permanent goal is to maximize future expected reward, using the (alternative) target theorem (3). Part thereof is to avoid hunger. There is nothing in its fridge, and shops close down at 8.30pm. It does not have time to optimize its way to the supermarket in every little detail, but if it does not get going right now it will stay hungry tonight (in principle such near-future consequences of actions should be easily provable, possibly even in a way related to how humans prove advantages of potential actions to themselves). That is, if the agent's previous policy did not already include, say, an automatic daily evening trip to the supermarket, the policy provably should be rewritten at least in a very limited and simple way right now, while there is still time, such that the agent will surely get some food tonight, without affecting less urgent future behavior that can be optimized / decided later, such as details of the route to the food, or of tomorrow's actions.

7. In certain uninteresting environments reward is maximized by becoming dumb. For example, a given task may require to repeatedly and forever execute the same pleasure center-activating action, as quickly as possible. In such cases the Gödel machine may delete most of its more time-consuming initial software including the proof searcher.

8. Note that there is no reason why a Gödel machine should not augment its own hardware. Suppose its lifetime is known to be 100 years. Given a hard problem and axioms restricting the possible behaviors of the environment, the Gödel machine might find a proof that its expected cumulative reward will increase if it invests 10 years into building faster computational hardware, by exploiting the physical resources of its environment.

Next: Example Applications Up: Discussion & Previous Work Previous: Discussion & Previous Work
Juergen Schmidhuber 2005-01-03