Logic Exercises What is wrong with the following proof: Suppose that $x = y$ then: $\Rightarrow x^2 = xy$ $\Rightarrow x^2 - y^2 = xy - y^2$ $\Rightarrow (x + y)(x - y) = y(x - y)$ $\Rightarrow x + y = y$ $\Rightarrow 2y = y$ $\Rightarrow 2 = 1$