2 = 1

A friend's Facebook status reminds me of this silly proof of 2 = 1:

a = b
a² = ab
a² - b² = ab - b²
(a + b)(a - b) = b(a - b)
a + b = b
a + a = a (as we suppose a = b in the beginning)
2a = a
2 = 1

:P