I am new to Mathematica so please excuse what may be a simple question. I tried to reproduce an example 3D plot from the documentation and got no plot using the function `ContourPlot3D[x^3+y^2-z^2==0,{x,-2,2},{y,-2,2},{z,-2,2}]. I have attached a screen shot with my unsuccessful attempt. What am I missing? 
Thanks!
