Not signed in

Want to take part in these discussions? Sign in if you have an account, or apply for one below

• Username
• Password
• Remember me

• Sign in using OpenID
• Remember me

• Forgot your password?
• Apply for membership

2-category 2-category-theory abelian-categories adjoint algebra algebraic algebraic-geometry algebraic-topology analysis analytic-geometry arithmetic arithmetic-geometry book bundles calculus categorical categories category category-theory chern-weil-theory cohesion cohesive-homotopy-type-theory cohomology colimits combinatorics complex complex-geometry computable-mathematics computer-science constructive cosmology deformation-theory descent diagrams differential differential-cohomology differential-equations differential-geometry digraphs duality elliptic-cohomology enriched fibration foundation foundations functional-analysis functor gauge-theory gebra geometric-quantization geometry graph graphs gravity grothendieck group group-theory harmonic-analysis higher higher-algebra higher-category-theory higher-differential-geometry higher-geometry higher-lie-theory higher-topos-theory homological homological-algebra homotopy homotopy-theory homotopy-type-theory index-theory integration integration-theory internal-categories k-theory lie-theory limits linear linear-algebra locale localization logic mathematics measure measure-theory modal modal-logic model model-category-theory monad monads monoidal monoidal-category-theory morphism motives motivic-cohomology nlab noncommutative noncommutative-geometry number-theory of operads operator operator-algebra order-theory pages pasting philosophy physics pro-object probability probability-theory quantization quantum quantum-field quantum-field-theory quantum-mechanics quantum-physics quantum-theory question representation representation-theory riemannian-geometry scheme schemes set set-theory sheaf simplicial space spin-geometry stable-homotopy-theory stack string string-theory superalgebra supergeometry svg symplectic-geometry synthetic-differential-geometry terminology theory topology topos topos-theory tqft type type-theory universal variational-calculus

1. • CommentRowNumber1.
   • CommentAuthorjesse
   • CommentTimeMar 8th 2017
   • (edited Mar 8th 2017)
   • PermaLink
   Author: jesse
   Format: MarkdownItexCreated [[Fraïssé limit]]. (I was pleasantly surprised to see @David_Corfield had [posted](https://golem.ph.utexas.edu/category/2009/11/fraisse_limits.html) about the these things a while ago for the n-Category Cafe.) Mentioned a neat result of Olivia Caramello's that [[omega-categorical]] structures presentable as Fraisse limits are determined by their automorphism groups $G$ with the topology of pointwise convergence in a very nice way: their [[classifying topos|classifying toposes]] are precisely the toposes of continuous $G$-sets. To fill in a grey link, I also created an entry for the [[countable random graph]].

   Created Fraïssé limit.

   (I was pleasantly surprised to see @David_Corfield had posted about the these things a while ago for the n-Category Cafe.)

   Mentioned a neat result of Olivia Caramello’s that omega-categorical structures presentable as Fraisse limits are determined by their automorphism groups $G$ with the topology of pointwise convergence in a very nice way: their classifying toposes are precisely the toposes of continuous $G$-sets.

   To fill in a grey link, I also created an entry for the countable random graph.

2. • CommentRowNumber2.
   • CommentAuthorDavid_Corfield
   • CommentTimeMar 8th 2017
   • PermaLink
   Author: David_Corfield
   Format: MarkdownItexI hope the discussion at the Cafe got things right in the end. I recall plenty of terminological confusion about what kind of limits and embeddings were involved. I see my [follow-up](https://golem.ph.utexas.edu/category/2010/01/looking_for_compatible_structu.html) didn't generate much discussion.

   I hope the discussion at the Cafe got things right in the end. I recall plenty of terminological confusion about what kind of limits and embeddings were involved.

   I see my follow-up didn’t generate much discussion.