$$\begin{align} x &= y \newline x^2 &= xy \newline x^2 -y^2 &= xy -y^2 \newline (x+y)(x-y) &= y(x-y) \newline x+y &= y \newline y + y &= y \newline 2y &= y \newline 2 &= 1 \end{align}$$

To Do: find a more compelling version and make interactive