[From Oded Maler 920807]

[Rick yesterday:]

I hope that you (Oded) or Eric can find the time to explain some ALife project

in detail and show how it relates to PCT.

Sorry to disappoint you but like MR HARNDEN (whose general attitude

seems to be like mine) I'm not an active member of the alife community

(except for a paper on my worm rejected from the first ECAL, which I

attended, and except for my bad habit of tracking "trendy" branches of

"science"). You might get idea of their work from looking at their

proceedings (usually edited by Langton, Addison-Wesley) - I'm sure

you'll find non-references to PCT almost in every page

Since you mentioned complex dynamics, I recall hearing in Aix a talk

by Kugler about changing observables and all that. Do you have any

opinion (surprising or not, it doesn'r matter) on this stuff?

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Concerning the Astro discussion, since I'm interested in an area

which might be called "specification and verification of non-living

syatems" I would like to ask what do you think will be an appropriate

specification of the properties of the Mother-Astro systems. That is,

I'm looking for something of the form:

Given that:

1) some properties of engines (gains), sensors (delays)

2) some restriction on the patterns of movement of Mother (e.g.,

it will not switch from positive speed of light to negative one

too often)

3) some limitation on the noise (maybe a property of sensors and

actuators)

Then:

e.g.,:

1) there will be some moment t where the distance remains

smaller than d

2) for every time t when distance is bigger then d there is t'>t

where distance is smaller then d.

3) for every interval the integral/average of distance is

smaller than d.

I'm interested in developing methods for giving formal proofs for

such properties (at this stage mathematical control theory seems to

be sufficient but when discrete events appear, e.g., Mother is turning

into a Monster (like in PacMan) it becomes more complicated.)

Thanks

--Oded