# Assignment 4

Common mistakes:

• On 3.56, many students proved the base case for $n=3$. But since the question is to prove for all natural numbers, you should prove the base case for $n=1, 2$.
• On 12.19, many students forgot the base case for $n=0$.
• On 4.13, Some students get the digits for $x$ as $a-c-1, 9, 10-(a-c)$ without the assumption that $a>c$.