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For questions requesting examples of a certain structure or phenomenon

5 votes

What's an illustrative example of a tame algebra?

For the Kronecker quiver (two vertices, two arrows in the same direction) and dimension vector (1,1), over an algebraically closed ground field, the indecomposables are naturally parameterized by poin …
Mike Pierce's user avatar
  • 1,161
6 votes

Nonfree projective module over a regular UFD?

What about $R = \mathbb R[x,y,z]/\langle x^2+y^2+z^2-1\rangle$ and $M$ the projective module corresponding to the tangent bundle? This seems to satisfy your criteria except probably for factorialness …
Hugh Thomas's user avatar
  • 6,302
5 votes
Accepted

Is there a poset with 0 with countable automorphism group?

It seems unlikely (once you assume d.c.c.). Define the height of an element $x$ in $P$ to be the length of the shortest unrefinable chain from $x$ to $0$. Let $P_n$ denote the elements of $P$ whos …
Hugh Thomas's user avatar
  • 6,302
7 votes

Examples of noncommutative analogs outside operator algebras?

There is a notion of non-commutative resolution of a singularity (in the sense of commutative algebraic geometry). See section 5 of this ICM talk by Bondal and Orlov. The following is a simple exa …
Hugh Thomas's user avatar
  • 6,302
7 votes

What are examples of good toy models in mathematics?

Derived categories of finite dimensional hereditary algebras for other derived categories. (Though under good circumstances other derived categories can turn out to be equivalent to derived categorie …
Hugh Thomas's user avatar
  • 6,302