Question: How do I plot two intersecting surfaces

I'm trying to plot the region bounded by the coordinate planes, the plane z=2-y and the cylinder x=4-y^2

This is what I have so far.  I want to know how to get rid of the portions of the planes and cylinder that are not enclosing the region.

restart;

with(plots);

xmin := 0;
xmax := 4;
ymin := 0;
ymax := 2;
zmin := 0;
zmax := 2;

a := plot3d([2-y], x = xmin .. xmax, y = ymin .. ymax, orientation = [40, 70], transparency = 0, color = green, filled = false, title = "");
%;

b := implicitplot3d([z = 0, y = 0, x = 0], x = xmin .. xmax, y = ymin .. ymax, z = zmin .. zmax, transparency = .5, axes = normal);
%;
c := implicitplot3d([x = -y^2+4], x = xmin .. xmax, y = ymin .. ymax, z = zmin .. zmax, transparency = .5, filled = true, axes = normal, color = blue, orientation = [45, 35]);

display(a, b, c);