0<=x<=1
0<=y<=1
0<=z<=x/(1+y)

[x y]=meshgrid(0:0.01:1);
z=x./(1+y);
surf(x,y,z);

[X,Y,Z]=meshgrid(0:.01:1);

isosurface(X,Y,Z,Z.*(X./(1+Y)-Z),0)

isosurface(X,Y,Z,Z.*(X./(1+Y)-Z).*X.*(X-1).*Y.*(Y-1),0)