**4A:** Give a proper proof by induction that the *k*th entry of the *n*th row of Pascal's triangle is "*n* choose *k*". Take as the *definition* of Pascal's triangle the constructive description given on page 92 of the text.

**Extra Credit:** Section 14, #21.
Your output may be in simple ASCII, and may use *'s or something similar. An equispaced font is required. This problem will be worth about 10 bonus points (half an assignment), and these points are independent of your score on this assignment. Please print out your picture and your source code and submit them to me directly (do not attach to Assignment #4).

**Warning:** This assignment is **not** compatible with last semester's version of the text!

### Assignment #3 (due Wed. 2/10):

**Section 6 (pg 37):** 7, 10

**Section 14 (pg 96):** 3, 10, 12, 13