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visits member for 1 year, 7 months
seen Aug 23 at 9:34

Jul
2
awarded  Curious
May
29
revised $\mathcal U$ Grothendieck universe. Is $\mathcal{P(U)}$ a model for NBG?
small typo corrected
May
15
comment Hartshorne Problem 1.2.14 on Segre Embedding
Shouldn't you prove that $\mathfrak a$ is actually a homogeneous ideal?
May
14
comment When is $N\otimes_A B \to N$ an isomorphism?
Oh, I think I see: $f$ is also epi iff $B \to B \otimes_A B$ is iso; tensoring by $N\otimes_B-$ (which, as functor, preserves isos) and using the associativity of tensor product we are done.
May
14
comment When is $N\otimes_A B \to N$ an isomorphism?
Nice! Formal because $\colon A \to B$ is epi iff $b\otimes 1_B = 1_B \otimes b$ in $B\otimes_A B$? Or it's even simpler?
May
14
revised When is $N\otimes_A B \to N$ an isomorphism?
edited body
May
14
asked When is $N\otimes_A B \to N$ an isomorphism?
Apr
24
revised Working out the normalization of $\mathbb C[X,Y]/(X^2-Y^3)$.
fixed small typo
Apr
24
suggested suggested edit on Working out the normalization of $\mathbb C[X,Y]/(X^2-Y^3)$.
Apr
17
comment Are $R=K[a,b,c,d]/(ad-bc, a^2c-b^3, bd^2-c^3, ac^2-b^2d)$ and $K[x^4,x^3y,xy^3,y^4]$ isomorphic?
Great answer! A couple of questions: i) shouldn't it be $I = (a-x^4, \dots )$? ii) is the variable $z$ really needed?
Apr
14
comment Incidence variety fo Grassmmanians
I don't think this is a morphism of varieties, otherwise you could prove, adapting the map, that every subset of a variety should be closed.
Mar
22
accepted Reflexivity of equality in sequent calculus
Mar
10
revised Reflexivity of equality in sequent calculus
Edit: cut rule
Mar
10
asked Reflexivity of equality in sequent calculus
Jan
16
awarded  Yearling
Oct
30
accepted Ring and $A$-module, but not $A$-algebra
Oct
30
asked Ring and $A$-module, but not $A$-algebra
Jun
29
comment A little confusion about extensions $E(-,-)$ and $\mathrm{Ext}(-,-)$
It is rather a feeling and I may mistake, but I suppose what changes is the projection $\pi_i \colon \mathbb Z \to \mathbb Z/(p)$.
Jun
29
comment Developing category theory inside ETCS
Universe in a topos. Note that this formulation is stricly relating to Zhen Lin's answer.
Jun
29
comment Developing category theory inside ETCS
In Lawvere's world, $\mathcal C_i, i=1, 2$ live in ETCC. Actually, you need less than all ETCC to formalize ETCS. Take a curious look at this page on nlab. As you can see, axioms are really easy.