restart;
with(plots):
with(plottools):
addcoords(z_cylindrical_elliptical,[z,r,phi],[r*cos(phi),1/sqrt(3)*r*sin(phi),z]);
a:=implicitplot3d(x^2=y,x=0..2,y=0..1,z=0..4, axes=normal, color=red):
b:=implicitplot3d(x=y^2,x=0..2,y=0..1,z=0..4, axes=normal, color=red):

```
c:=plot3d(r^2,r=0..2,phi=0..Pi/2,coords=z_cylindrical_elliptical,
title=`elliptisches Paraboloid`,axes=normal,labels=["x","y","z"], scaling=constrained, color=blue,style=wireframe):
d:=plot3d(0,x=0..2,y=0..2, axes=normal, style=wireframe, color=green):
display({a,b,c,d});
How can I get maple to plot a function
that fullfills the following restrictions.
if z
```