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 * [ ] Study Section 35.5 of the textbook.
 * [ ] Do Exercises 35.5-2 and Problem 35-3 from the textbook as part of Assignment 4.
+
+# Divide-and-Conquer
+
+We solve a problem recursively, applying three steps at each level of the
+recursion.
+
+1. Divide the problem into a number of subproblems that are smaller instances of the same problem.
+1. Conquer the subproblems by solving them recursively. If the subproblem sizes
+   are small enough, however, just solve the subproblems in a straightforward
+   manner.
+1. Combine the solutions to the subproblems into the solution for the original problem.
+
+When the subproblems are large enough to solve recursively, we call that the
+*recursive case*. Once the subproblems become small enough that we no longer
+recurse, we say that the recursion "bottoms out" and that we have gotten down to
+the *base case*.
+
+## Recurrenes
+
+Give us a natural way to characterize the running times of divide and conquer
+algorithms. A *recurrence* is an equation or inequality that describes a
+function in terms of its value on smaller inputs.