I say yes because there is only one z letter in the equation.
Echoing HallsofIvy's response, how are you defining a function? In the equation, for example, $\displaystyle z^2 = y$ there is "only one z in the equation" but my example is not a function.
Echoing HallsofIvy's response, how are you defining a function? In the equation, for example, $\displaystyle z^2 = y$ there is "only one z in the equation" but my example is not a function.