I don't understand why it is equivalent to $x=z$ and $x\neq0$, and not equivalent to:
$x=z$, $x\neq0$ and $y\neq0$. $y$ can't be equal to $0$ in order for $R^2$ to be true.
I don't understand why it is equivalent to $x=z$ and $x\neq0$, and not equivalent to:
$x=z$, $x\neq0$ and $y\neq0$. $y$ can't be equal to $0$ in order for $R^2$ to be true.