bio | website | |
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location | Rennes, France | |
age | 62 | |
visits | member for | 3 years, 9 months |
seen | 2 hours ago | |
stats | profile views | 4,027 |
Apr 6 |
awarded | Nice Answer |
Mar 28 |
comment |
Relation between dimension of Proj(S) and dimension of S
In the definition of Proj, don't you want $P$ to be graded? |
Mar 27 |
comment |
Is $G_{\operatorname{red}}$ normal in $G$?
@user76758: in fact, you get exactly my example "in nature" with your construction by taking for $H$ the group of affine automorphisms of the line (except this $H$ is not semisimple). |
Mar 27 |
answered | Is $G_{\operatorname{red}}$ normal in $G$? |
Mar 20 |
comment |
Is the category of schemes wellpowered? regularly wellpowered?
Unfortunately, a morphism of affine schemes which is a regular mono of schemes (i.e. an immersion) is not necessarily a regular mono in $\mathbf{Aff}$ (i.e. a closed immersion). |
Mar 20 |
awarded | Nice Answer |
Mar 20 |
comment |
Is the category of schemes wellpowered? regularly wellpowered?
You can take $I=\vert Y\vert$ (the underlying space of $Y$, which is smaller than $\vert X\vert$). For each $y\in I$, choose $V_y$ and $U_y$ such that $y\in V_y$. (We don't need the $U$'s to cover $X$). |
Mar 19 |
answered | Is the category of schemes wellpowered? regularly wellpowered? |
Mar 19 |
comment |
Is the category of schemes wellpowered? regularly wellpowered?
But this implies the same property for the category of schemes; in fact this is stated here but I could not find a proof there, so I am giving one in a second answer. |
Mar 19 |
comment |
Is the category of schemes wellpowered? regularly wellpowered?
Do you have a reference for the wellpoweredness of $\mathbf{Aff}$? |
Mar 18 |
comment |
Is the category of schemes wellpowered? regularly wellpowered?
The quasicompact (or reduced) assumption is needed to embed $Y$ as an open subscheme of a closed subscheme of $X$. To factor the oher way, there is no condition (and this follows easily from the definition of an immersion). |
Mar 18 |
revised |
Is the category of schemes wellpowered? regularly wellpowered?
edited body |
Mar 18 |
answered | Is the category of schemes wellpowered? regularly wellpowered? |
Mar 14 |
awarded | Nice Answer |
Mar 2 |
awarded | Nice Answer |
Feb 13 |
comment |
Bertini type theorem
And when $\dim X>1$, the argument shows that $f_{\vert X\cap H}$ is nonconstant for every $H$. |
Feb 11 |
awarded | Good Answer |
Jan 26 |
comment |
Tensor powers of an algebra all isomorphic
"Which means $A\subset K$": yes assuming e.g. that $k$ is a domain and $A\neq0$. In fact, the zero algebra is a counterexample to many claims. Also, "finitely presented" is irrelevant, I think. |
Jan 23 |
awarded | ag.algebraic-geometry |
Jan 22 |
answered | 'Cohomologically approximating' a $\mathbb{Q}[[t]]$-scheme by a one over the henselization of $\mathbb{Q}[t]$? |