> restart;

> x:=cos(t);

> y:=sin(t);

> z1:=x;

> z2:=-x;

> z:=(1-s)*z1+s*z2;

> a:=plot3d([x,y,z],s=0..1,t=0..2*Pi,scaling=constrained,color=yellow):

> b:=plot3d([z,y,x],s=0..1,t=0..2*Pi,scaling=constrained,color=green):

> with(plots):

Warning, the name changecoords has been redefined

> c:=display(a,b):

> display(c);

Error, unexpected number

> with(plottools);

> vrml(c,"c:/My Documents/mei/10.html/10-1.wrl",background_color=white):

>