A classic puzzle

This is an old puzzle, but interesting if you haven't heard it before.

A hunter walked one kilometer south from his camp. Then he walked one kilometer west. There he shot a bear. Then he walked one kilometer north, and found that he was back at his camp. What color was the bear?

The answer can be found here. A lot more puzzles collected by the same guy can be found here.

Proof that 2 = 1

a=b
a²-b²=ab-b²
(a+b)(a-b)=b(a-b)
a+b=b
2b=b
2=1

Can you see the problem?