Topics in Combinatorics

This course will mainly focus on various counting techniques and problems arising in the context of hyperplane arrangements. We shall also discuss order theoretic structures, Mobius inversion, incidence algebras and the Euler characteristic. Throughout the course Coxeter arrangements (that arise due to actions of finite reflection groups) and their deformations will serve as runnning examples.

By the end of the first month everybody is expected to choose their project topic.


Line arrangements and some classical problems, posets and Mobius inversion, hyperplane arrangements, deletion-restriction, Zaslavsky's theorem, graphical arrangements, matroids, the finite field method, ESA, interval order, Shi and Catalan arrangements, free arrangements.


  • Days: Mondays and Firdays
  • Time: 09:10 - 10:25 am
  • Place:  LH 4
  • Office hours: by appointment
  • Prerequisites: Algebra 2 and/or permission of the instructor/ faculty advisor


  1. A mini course on hyperplane arrangements by Richard Stanley. Web link
  2. Enumerative Combinatorics (volume 1) by Richard Stanley. (Chapter 3)
  3. Introduction to geometric probability by D. Klain and G.-C. Rota

Teaching Assistants

  1. Bishal Deb
  2. Paramjit Singh


  • Assignments: 30%
  • Project: 40%
  • End sem exam: 30%



The assignments will be posted on this page. It is your duty to submit the solutions on time. Copying and/or plagiarism will not be tolerated. Here are a few writing guidelines you might want to follow.

  1. Feel free to work together, but you should submit your own work.
  2. Your questions/comments/suggestions are most welcome. I will also be fairly generous with the hints. However, do not expect any kind of help, including extensions, on the day a homework is due.
  3. Please turn in a neat stapled stack of papers. Refrain from using blank / printing paper. Use ruled paper.
  4. Your final finished version should be as polished as you can make it. This probably means that you cannot submit sketchy solutions or sloppily written first versions. Please expect to do a fair amount of rewriting. Do not hand in work with parts crossed out; either use a pencil and erase or rewrite.
  5. Please write complete sentences that form paragraphs and so forth. It might be a good idea to use short simple sentences; avoid long complicated sentences.
  6. Do use commonly accepted notation (e.g., for functions, sets, etc.) and never invent new notation when there is already some available.
  7. Make sure you provide a statement clearly indicating precisely what it is that you are about to prove. You can, if you want, label your statement as a Theorem or Claim or whatever. Write the word Proof, and then give your proof.
  8. Throughout your writing, constantly tell the reader (i.e. me, :-)) exactly what it is that you are about to demonstrate. Be sure to indicate the end of your proof.
  9. Your answers should combine “logic”, your hypotheses, and possibly other mathematical facts (e.g., theorems that we have proved in class) into an argument that establishes the asserted conclusion.
  10. Please be extra careful about the order in which you use your quantifiers.
  11. In your arguments you can make free use of anything that we have proven in class, and of course all logic rules and basic axioms and definitions. Anything else that you use should be proved.


Assignments Due date
Assignment 1
Assignment 2
Assignment 3
Assignment 4