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Chris Grossack's Blog

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Chris Grossack's math blog and professional website.

Math

’20’21’22’23’24’25’26
Posts
114 from 3 Aug 2020 to 20 Mar 2026
Posting
monthly (6 in the last year)
Kind
personal blog
Feed
https://grossack.site/feed.xml

2026 6

  1. Is a Random Perfect Group Nontrivial?
  2. Is a Random Perfect Group Nontrivial?
  3. Talk -- Factorization Homology and Quantum Character Stacks
  4. An Overly Explicit Computation with Character Stacks
  5. main post
  6. An Overly Explicit Computation with Character Stacks

2025 19

  1. $F_2 \times F_2$ is Incoherent -- A Polite Spectral Sequence Computation
  2. $F_2 \times F_2$ is Incoherent -- A Polite Spectral Sequence Computation
  3. Free Things Are Complicated (Especially the Sphere Spectrum!)
  4. Free Things Are Complicated (Especially the Sphere Spectrum!)
  5. An Explicit Computation in Derived Algebraic Geometry
  6. An Explicit Computation in Derived Algebraic Geometry
  7. Explicitly Computing The Action Lie Algebroid for $SL_2(\mathbb{R}) \curvearrowright \mathbb{R}^2$
  8. How to Explicitly Compute Charts for a Levelset Submanifold
  9. Sl2 action algebroid computation
  10. How to Explicitly Compute Charts for a Levelset Submanifold
  11. A Proof that there's No Constructive Proof of the Intermediate Value Theorem
  12. A Proof that there's No Constructive Proof of the Intermediate Value Theorem
  13. An Empty Product of Nonempty Sets
  14. An Empty Product of Nonempty Sets
  15. Analytic Combinatorics Redux
  16. Analytic Combinatorics -- A Worked Example
  17. Some Doodles I'm Proud of -- The Capping Algorithm for Embedded Graphs
  18. A Cute Application of the Yoneda Lemma
  19. Where Do Those Undergraduate Divisibility Problems Come From?

2024 8

  1. $\mathsf{B}\text{Diff}(\Sigma)$ Classifies $\Sigma$-bundles
  2. Finiteness in Sheaf Topoi
  3. Life in Johnstone's Topological Topos 3 -- Bonus Axioms
  4. Life in Johnstone's Topological Topos 1 -- Fundamentals
  5. Life in Johnstone's Topological Topos 2 -- Topological Algebras
  6. Talk -- What is Factorization Homology?
  7. Proving Another "Real Theorem" with Topos Theory
  8. Internal Group Actions as Enriched Functors

2023 7

  1. Talk -- 2-Categorical Descent and (Essentially) Algebraic Theories
  2. A truly incredible fact about the number 37
  3. Preprint -- The RAAG Functor as a Categorical Embedding
  4. Estimating a Difference of Products
  5. Talk -- What is Algebraic Geometry and Why Should You Care?
  6. A Quick Application of Model Categories
  7. Building Objects with Category Theory

2022 22

  1. Externalizing Some Simple Topos Statements
  2. Talk - Where Are The Open Sets?
  3. Monoidal Monoidoidoids
  4. Embedding Dihedral Groups in Vanishingly Small Symmetric Groups
  5. Why Care about the "Homotopy Theory of Homotopy Theories"? (Homotopy Theories pt 4/4)
  6. An Interlude -- Quasicategories (Homotopy Theories pt 3/4)
  7. Why Care About Infinity Categories? (Homotopy Theories pt 2/4)
  8. What are Model Categories? (Homotopy Theories pt 1/4)
  9. Chain Homotopies Geometrically
  10. Locale Basics
  11. How many symbols can $f'(x)$ have if $f$ has $n$ symbols?
  12. Using Geometry in Logic
  13. How Holomorphic Functions are Just Like Polynomials
  14. Why is the Completion of a Local Ring "More Local" than just Localizing?
  15. Talk (?) -- Why Care about Lie Algebras?
  16. Talk -- Let's Solve a Simple Analysis Problem. Together.
  17. Talk (?) -- Universal Enveloping Algebras
  18. A New (to me) Perspective on Jordan Canonical Form
  19. Automatic Asymptotics with Sage
  20. An Explicit Example of the Proof of the Nullstellensatz
  21. A Follow Up -- Explicit Error Bounds
  22. Using Probability to Make Difficult Limits Obvious

2021 39

  1. Rational maps $\mathbb{P}^1 \to \mathbb{P}^n$ are automatically regular
  2. Slaughtering Competition Problems with Quantifier Elimination
  3. Some Questions about the Mathematics of Hitomezashi
  4. Topological Categories -- A Unifying Framework
  5. A Hitomezashi Maker
  6. Talk - The Weil Conjectures and Topos Theory
  7. Using Ultrapowers to Solve Problems
  8. Talk - The Univalence Axiom
  9. Dense Pythagorean Triples -- A Cute Problem in Arithmetic Geometry
  10. Talk - Bring Out the Crayons -- A Survey of Descriptive Combinatorics
  11. What Do Wirtinger Derivatives Do?
  12. A Nonarithmetic Example of a Noneuclidean Principal Ideal Domain
  13. Talk - Top $5$ Undecidable Problems -- Number $4$ will shock you!
  14. Qual Recap
  15. Interlude -- The Baire Category Theorem
  16. Hilbert Spaces
  17. Banach Spaces and Preserving Finite Dimensional Theorems
  18. Examples of Syntax/Semantics Theorems Throughout Math
  19. $L^p$ Spaces
  20. Measure Theory and Differentiation (Part 2)
  21. Showing There is No Element of Some Order in a Group
  22. A geometric proof that $D_{2m} \leq \mathfrak{S}_n$ is possible for $m > n$
  23. Solving Solvable Polynomials with Galois Theory (Part 1)
  24. Iteration Asymptotics
  25. How Many Group Structures on a Set?
  26. A Wild Arctan Formula
  27. Making Pretty Pictures for Galois Theory
  28. Finite Calculus, Stirling Numbers, and Cleverly Changing Basis
  29. Reducing to $\mathbb{Z}$ -- Permanence and Concrete Proofs
  30. Two Sage Visuals
  31. Remembering the Reverse Triangle Inequality
  32. Checking Concavity with Sage
  33. Talk - Problem Solving Without Ansibles -- An Introduction to Communication Complexity
  34. Talk - Categories, Modalities, and Type Theories: Oh My
  35. Cohomology Intuitively
  36. Linearly Ordered Groups and CH
  37. Sage Sums
  38. Measure Theory and Differentiation (Part 1)
  39. Talk - Why Think -- Letting Computers do Math for Us

2020 13

  1. Talk - Syntax and Semantics (Trans Math Day 2020)
  2. Automorphisms Don't Extend
  3. Talk - Programming and Category Theory
  4. Quantitative Cesaro Sums
  5. Limsups and Liminfs of Sets
  6. Nilpotentizing Groups
  7. $H_1 \cong H_2$ doesn't mean $G / H_1 \cong G / H_2$!
  8. Talk - Model Theory and You
  9. Submodels vs Elementary Submodels
  10. Existence through Fixed Points
  11. Lower Bounds from Closed Sets
  12. Right Angled Artin Groups
  13. Visualizing Hyperbolic Isometries