C9 Conversations: Yuri Gurevich On Logic, Imperative, Abstraction and Algorithms
- Posted: Feb 09, 2010 at 12:10 PM
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Welcome to the latest installment of C9 Conversations. For this episode, we were very fortunate to get a chance to converse openly with one of the world’s preeminent mathematical logicians, the great Yuri Gurevich.
Dr. Gurevich is Professor Emeritus of Electrical Engineering and Computer Science at the University of Michigan. He is currently a principle research scientist in Wolfram Schulte’s RiSE team (Research in Software Engineering group at Microsoft Research).
Originally, Dr. Gurevich started his career as an algebraist. Later he became a logician. Then he moved to computer science, where his main projects have been Abstract State Machines, Average Case Computational Complexity, and Finite Model Theory. Dr. Gurevich
has been honored as a Dr. Honoris Causa of the University of Limburg, Belgium (1998), as a Fellow of the Association for Computing Machinery (1996), as well as a Fellow of the John Simon Guggenheim Memorial Foundation (1995).
Dr. Gurevich's fundamental work on the theory of
Abstract State Machines (ASMs) is of paramount importance for theoretical and applied computer science. The significance of the theoretical concepts developed by Gurevich is confirmed by the substantial impact they have on mathematical modeling of discrete
dynamic systems.
*This is probably the only interview in C9's history where a good case is made for
imperative programming versus declarative and functional (this starts right off the bat at around 02:31).
Read
Yuri's Annotated Articles
Tune in. Meet Yuri Gurevich.
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Hi Charles,
Could you please visit him again, some time and have a good interview... please... please... You caught him totally unprepared and I would love to hear more of his work. Very interesting Interview... and looking forward to see him again on C9.
Hi,
Thanks for the comment. I'll try to get Yuri into the C9 studio for some deep dives on specific logical/mathematical/computational subject matter... This particular interview is not a technical interview (there is no preparation requirement for the interviewee, by design, in this context...), but rather a conversation with a master logician with a very interesting and rich history in computer science.
C
Thanks Charles... I really appreciate it.
This is quite cool, thanks Charles. Reminds me of the good old C9
Right on. I will be doing more of the Old School. Glad you picked up on this
C
I like these abstract topics. If anyone was looking for the DKAL paper, here it is.
Very nice interview and what a great man!!!
I just have one small suggestion here... With all respect to the interviewer, when someone like Yuri is the interviewee, it's better to have someone who is close to him and having an angle on theoretical computer science. What happens here is that, the discussion starts with a divide and both the parties are slowly bridging the gap. Yuri is trying to be as simple as possible, trying to materialize questions in his own format, checking to see how good the question is, whether the question is a genuine one OR is it something that seems genuine, but actually is by chance making him think so. So that's why he is not able to go at a pace he likes. If the interviewer was someone close to Yuri, then he knows that this guy (the interviewer) is someone who understands his language and that makes the conversation seamless OR friction less. That makes the interview more enjoyable for people who understand what Yuri is taking about. Trust me; if someone who understands Yuri's language sees this interview, he is going to have the same difficulties that Yuri is facing in the interview.
Hope my theory is understood
, But anyway Charles, you have done a good job, appreciate it a lot.
Thanks mate... a very good technical paper and explanation is outstanding... After reading the paper, I was wondering what is cooking based on his works... Hopefully Charles will find him and do very good interview
I remember the rather softly spoken Yuri from the interview with Betrand Meyer, so this is a welcome revisit.
Greetings from the niners Yuri!
It would be great to have him back for a deeper discussuin.
I really like the conversational tone. There's space for both, we can have the faux studio interviews with sofas, potted plants and 3 point lighting setups - and then we can have these more conversational pieces. I like them because there's more humanity in them and I find myself almost as interested in trying to find out how this person could have arrived at their ideas (perhaps through reseach, perhaps through life, or both) as I am in the ideas themselves. I think the more informal location helps bring this out. Let's have both studio and ad-hoc, variety, that's the thing...
Thanks for the feedback. Originally, I had thought this should be an E2E, but the goal here is not to be over technical and really learn about the person being interviewed. For sure, somebody like me conversing with somebody like Yuri is more of an I2E (idiot to expert), but I think it works as the focus is on the interviewee, not the interviewer. That said, it is clear that we need to get Yuri again to dig into some very technical subject matter. Yuri seemed quite pleased with the 9 experience, so this should be possible.
C
Thanks for the feedback. C9 Conversations are, by explicit design, conversations. I am no expert in Yuri's field (not many folks are, actually, when you think about it...), but I am a technical generalist. Sometimes it's good to have a generalist-to-expert conversation. That said, this would have made one hell of an E2E, too
C
Is this the paper referenced in the conversation?
When are two algorithms the same?
Yes sir.
C
It looks like Yuri argues that input/output is not the only aspect of an algorithm of importance; although in a mathematical sense this is precisely what matters [as the good Dr. Beckman has taught us], but then again, time and space is not of the same relevance there - memory use and performance.
It's quite natural that one cannot talk about whether two objects are equivalent (be they algorithms, pencils or peanuts), so without any abstract notion of equivalence, all things are distinct. The question is more when these distinctions matter and when not.
One might consider the memory use as part of the output of a program, declarative or imperative. In the declarative case the compiler then plays a larger role because it more radically rearranges the program (the what becomes the how). Thereby one might say that a program is only correct (or not) (according to some performance or memory constraints) when combined with a particular compiler, garbage collector, physical or virtual machine, etc.
At some low level functions are expressed imperatevely, you need to address the "How" you can't always live in the abstract world.
Until there are some hardware changes we have to start from imperative programming and then create abstractions for declarative and functional programming.
Now the imperative part can be small so it is easier to debug, test, reason about it and the rest can be declarative. (easier said than done
)
That's a matter of course. Is there a lambda machine out there?
From what I've heard in talks given by Simon Peyton-Jones (MS Research, GHC developer), projects to build graph reduction processors in the past were not very successful.
However, The Reduceron (a current project) might be interesting.
Edit: some slides (pdf)
Hey Yuri, amazing stuff. I could listen all day. Speaking of... it looked like there were some edits to cut down on length, I'd love to see the full thing if there is more. Thanks you guys.
The only things cut were me saying stupid things. You didn't miss anything.
C
Very interesting! Thank you for adding some depth and complexity to my understanding of operational semantics! I wonder if Yuri is aware of the connection between the lambda calculus, and therefore Haskell, and intuitionistic logic/constructive mathamatics through the Curry-Howard isomorphism?
That conversation worked out fairly well.
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