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- From: weemba@sagi.wistar.upenn.edu (Matthew P Wiener)
- Newsgroups: sci.math
- Subject: Re: Assorted questions and problems
- Message-ID: <96778@netnews.upenn.edu>
- Date: 9 Nov 92 16:14:40 GMT
- Article-I.D.: netnews.96778
- References: <BxDJ8v.DCw@world.std.com> <1992Nov8.181631.13298@Princeton.EDU>
- Sender: news@netnews.upenn.edu
- Reply-To: weemba@sagi.wistar.upenn.edu (Matthew P Wiener)
- Organization: The Wistar Institute of Anatomy and Biology
- Lines: 39
- Nntp-Posting-Host: sagi.wistar.upenn.edu
- In-reply-to: tao@fine.princeton.edu (Terry Tao)
-
- In article <1992Nov8.181631.13298@Princeton.EDU>, tao@fine (Terry Tao) writes:
- >I have three questions that I can't do. I hope you can see from the
- >diversity of them that they are not homework.
-
- Not just the diversity. They are on the deep side of things.
-
- >(1) what is the current status of the Bieberbach conjecture, that any
- >univalent holomorphic function f on the unit disk such that f(0) = 0 and
- >f'(0) = 1 satisfies the fact that the taylor expansion f(x) = \sum a_n x^n
- >has the property |a_n| \leq n? The last I heard, it was proved for n up to
- >7 only, and also for all n sufficiently large |a_n| \leq 1.08 n.
-
- It was proven in the mid-80s, amidst a good deal of confusion and some
- controversy. It's already in book form--see, eg, the AMS symposium.
-
- >(2) Suppose X and Y are Banach spaces. Can one construct a linear mapping
- >from X to Y which is NOT continous?e.g. a map from L^2 to L^2 which is not
- >bounded. Is it possible to construct one without AC?
-
- L^2 is a Hilbert space even--not a good example.
-
- This subject goes under the name of "automatic continuity". I have no
- idea of what happens without AC. The strongest you can prove in ZFC is
- the work of Bade--you can isolate a finite number of bad points. The
- work of Dales and Esterle gave counterexamples under CH. Woodin and
- Solovay showed that CH was necessary. See the book by Dales and Woodin.
-
- >(3) Assume the axiom of choice and the axiom of the continuum. Is it
- >true that two chains (totally ordered sets) which both have the
- >cardinality of the continuum have a one-to-one and onto order
- >preserving mapping betweem them?
-
- Of course not. It's almost embarrassing to mention the counterexamples,
- but here goes: (0,1) and [0,1]. The question you meant to ask, I assume,
- was if the orderings were dense. In that case, a back and forth argument
- shows the two are isomorphic. I'm pretty certain you need CH for this--I
- think Shelah has the contrary model.
- --
- -Matthew P Wiener (weemba@sagi.wistar.upenn.edu)
-