Is x=4 a function?

CPhill is of course correct but

y=4   IS  a  function.    

No.....it fails to pass the "vertical line test".......that is, when any vertical line is drawn on a graph, it can "cut" the function at only one point, and no more. But, x = 4 is a vertical line, so a vertical line laid on top of it would cut it at infinite points.....!!!!