117 reputation
16
bio website
location CHINA
age 27
visits member for 2 years, 8 months
seen Sep 1 '12 at 9:57
A graduate student.

Sep
24
awarded  Autobiographer
Apr
5
awarded  Yearling
Aug
29
awarded  Supporter
Aug
29
comment About Sigma_1 definability
Thank you for your comment!
Aug
29
comment About Sigma_1 definability
Thank you so much for your answer, it is very helpful for me. I have been on a travel without internet these days, so it is so late to reply your answer.
Aug
29
accepted About Sigma_1 definability
Aug
19
awarded  Editor
Aug
19
revised About Sigma_1 definability
added 7 characters in body
Aug
19
asked About Sigma_1 definability
Aug
4
accepted Definability of the direct limit
Aug
3
comment Definability of the direct limit
I just read the remark on iterated HOD classes in your paper. For the iterated ultrapower case, the graph is definable, but this does not happen in iterated HOD case. Thanks for your helpful answer again.
Aug
3
comment Definability of the direct limit
Thanks for your kind answer. If the entire system $<M_i|i<\omega>$ and $<j_{i,j}|i<j<\omega>$ are definable, then pick any representation of the direct limit, it is definable. But I still not well understand why the entire system is definable? $<M_i|i<\omega>$ is a sequence of classes, in general, an infinite sequence of classes need not be definable. But I have a feeling this sequence $<M_i|i<\omega>$ is similar to a sequence defined by induction, so whether "a sequence of classes defined by induction" is indeed definable?
Aug
3
asked Definability of the direct limit
Jul
21
awarded  Nice Question
Apr
7
comment A least model contains a given model and a given set
Thanks for your comments. I understand. If M is a proper class, then using closure of Godel's operations, there is a "closure" of $M\cup\{x\}$ as Jech' 13.24, which is an inner model of ZF. But if M is a set, then from the above link answer, such M[x] need not exist.
Apr
4
awarded  Scholar
Apr
4
accepted A subgroup intersects every conjugacy class
Apr
4
comment A subgroup intersects every conjugacy class
The example of upper triangular matrix is so standard, thank you for your example!
Apr
4
comment A subgroup intersects every conjugacy class
Thank you for your answer.
Apr
4
asked A least model contains a given model and a given set