Some notes I wrote in grad school while working through the text. I recommend only using them if you're really stuck: there may be errors, and writing solutions tends to be more educational than reading them. Last updated 1/19/17.
Injective modules are important critters in homological algebra with an (in my view) un-intuitive definition. These are notes about a slightly more concrete take on what it means to be an injective module.
An approach to solving recurrence relations via linear algebra.
Notes from an introductory talk on sheaves and abelian categories