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I will state it again. Given two rings R_1 and R_2 (with or without identity. It's not specified.). If R_1[x] is isomorphic to R_2[y] (No such requirement that the isomorphism sends the constant terms to constant terms), can we deduce that R_1 iso. to R_2?

I feel there might be a counterexample but it's quite hard to find one.

flag	asked Dec 8 2010 at 13:39 lethe 448●3●8

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This is the cancellation problem of Zariski. There are many counterexamples. See math.lsa.umich.edu/~hochster/Lip.text.pdf – J.C. Ottem Dec 8 2010 at 14:19

This (interesting) question has received many good answers on math.SE: math.stackexchange.com/questions/13504/…. I have voted to close it here as "no longer relevant". – Pete L. Clark Dec 9 2010 at 1:20

Tobias Kildetoft · Accepted Answer · 2010-12-08 13:44:28Z UTC

This was recently asked and answered at http://math.stackexchange.com/questions/13504/does-rx-cong-sx-imply-r-cong-s As answered there, it is possible to find two non-isomorphic commutative rings whose polynomial rings in one variable are isomorphic. An example is given in http://www.ams.org/journals/proc/1972-034-01/S0002-9939-1972-0294325-3/home.html

Steven Landsburg · Answer 2 · 2010-12-08 14:11:11Z UTC

Let X be an affine variety with two non-isomorphic vector bundles V and W that become isomorphic after adding a trivial line bundle to each. Then the coordinate rings of the total spaces of V and W should yield a counterexample. (Though you might have to do some extra work to verify that the total spaces of V and W are non-isomorphic as varieties.)

The counterexample cited by Tobias takes X to be the 2-sphere, V the tangent bundle to X, and W the trivial plane bundle over X.

Can we deduce that two rings R1 and R2 are isomorphic if their polynomial ring is iso.?

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