Re: [FOM] Poincaré Conjecture
joeshipman@aol.com
joeshipman at aol.com
Tue Jan 15 18:10:07 EST 2008
Now that it has been proved it is Delta^0. Previously it had been known
to be Pi^1; prior to Rubinstein's algorithm for recognizing the
3-sphere it was known to be Pi^2 (for all triangulated 3-manifolds X
together with a combinatorial reduction of Pi1(X) to the trivial group,
there exists a simplicial homeomorphism of X with the standard
3-sphere).
-- JS
-----Original Message-----
From: Apostolos Syropoulos <asyropoulos at gmail.com>
Provided that it makes sense to ask, does anyone have any idea where
in the arithmetical hierarchy would one put Poincaré's Conjecture? I
mean is it a \Pi_2 problem, a \Pi_3
problem or what?
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