# Martin Brandenburg

Münster, Germany

wwwmath.uni-muenster.de/u/m_bran11

Age: 26

PhD student interested in the interactions between algebraic geometry and category theory. More specifically, I "model" algebraic geometry on cocomplete symmetric monoidal categories.

Email: [my last name] [at] uni-muenster.de
 1h comment Existence of a faithfully flat algebra with a cancellation property@Will: $X=\mathrm{Spec}(\mathbb{Z})$, $A=\mathbb{Z}[1/2] \times \mathbb{Z}[1/3]$, $M=\mathbb{Z}$. 1h comment Question on a characterization of epimorphisms in $Sh(C)$ in terms of lifting along coveringsI assume that you are fimiliar with ordinary sheaves on top spaces? 2h comment Proving an extension is radicalYour $E$ is not normal. What is your def' of a radical extension? Do you know the main Thm of galois theory? 2h comment Is this an error on Wiki's "Exact sequence" page?A subobject is an equivalence class of monomorphisms (definition). Hence $A \to B$ represents a subobject. 2h answered How to use Nakayama's lemma here? 2h revised Is there a proof of the irrationality of $\sqrt{2}$ that involves modular arithmetic?added 137 characters in body 3h comment Hom-functor preserves pullbacksYes pullbacks are objects ... 4h comment Hom-functor preserves pullbacksErm. Perhaps you should learn basic set theory and the definition of the hom functor before dealing with pullbacks. 4h answered Is there a proof of the irrationality of $\sqrt{2}$ that involves modular arithmetic? 4h comment Hom-functor preserves pullbacks$X \times_S Y$ is the pullback of $X \to S \leftarrow Y$ (see any book, Wikipedia article, etc.) How do you denote the pullback? 4h comment Are there trials of finding a general solution for polynomials of $n^{th}$ degree with other operations?Hyperoperations are derived from the usual algebraic operations, so you won't get far with them. It is more interesting to ask for solutions which involve trigonometric functions, exponentials, logarithms etc. 4h comment Hom-functor preserves pullbacks(In particular don't waste your time in proving existence+uniqueness, show bijectivity directly) 4h answered Hom-functor preserves pullbacks 4h answered Compactness of $\operatorname{Proj}S$ 4h comment $\Bbb Q [ \sqrt{2} + \sqrt{3} ] = \Bbb Q [ \sqrt{2} , \sqrt{3} ]$en.wikipedia.org/wiki/Adjunction_%28field_theory%29 5h comment Right Engel GroupSorry, what is $[g,x,x]$? Is this $[[g,x],x]$? 5h revised What motivates the study of Abelian groups?added 254 characters in body 6h revised What motivates the study of Abelian groups?added 89 characters in body 7h comment What motivates the study of Abelian groups?@Asaf: ;-) .... nice joke 7h comment What motivates the study of Abelian groups?@Jack: Objects of arbitrary categories.