> front:=x->sqrt(x);
> rear:=x->1;
> left:=0; right:=1;
> n:=21;m:=9;
> top:=(x,y)->1-y;
> bottom:=(x,y)->0;
> xstep:=i->left+i*(right-left)/n;
> ystep:=(i,j)->front(xstep(i))+j*(rear(xstep(i))-front(xstep(i)))/m;
> Top:=[seq([seq([xstep(i), evalf(ystep(i,j)), evalf(top(xstep(i),ystep(i,j)))],j=0..m)],i=0..n)]:
> Bottom:=[seq([seq([xstep(i), evalf(ystep(i,j)), evalf(bottom(xstep(i),ystep(i,j)))],j=0..m)],i=0..n)]:
> Front:=[seq([[xstep(i), evalf(ystep(i,0)), evalf(bottom(xstep(i),ystep(i,0)))],[xstep(i), evalf(ystep(i,0)), evalf(top(xstep(i),ystep(i,0)))]],i=0..n)]:
> Rear:=[seq([[xstep(i), evalf(ystep(i,m)), evalf(bottom(xstep(i),ystep(i,m)))],[xstep(i), evalf(ystep(i,m)), evalf(top(xstep(i),ystep(i,m)))]],i=0..n)]:
> Left:=[[seq([xstep(0), evalf(ystep(0,j)), evalf(bottom(xstep(0),ystep(0,j)))],j=0..m)],[seq([xstep(0), evalf(ystep(0,j)), evalf(top(xstep(0),ystep(0,j)))],j=0..m)]]:
> Right:=[[seq([xstep(n), evalf(ystep(n,j)), evalf(bottom(xstep(n),ystep(n,j)))],j=0..m)],[seq([xstep(n), evalf(ystep(n,j)), evalf(top(xstep(n),ystep(n,j)))],j=0..m)]]:
> PLOT3D(MESH(Top),MESH(Bottom),MESH(Front),MESH(Rear),MESH(Left),MESH(Right));
>