> restart:

> p:=2*Pi/3:

> r1:=3+cos(t/3):

> x1:=r1*cos(t):

> y1:=r1*sin(t):

> z1:=sin(t/3):

> r2:=3+cos(t/3+p):

> x2:=r2*cos(t):

> y2:=r2*sin(t):

> z2:=sin(t/3+p):

> x:=(1-s)*x1+s*x2:

> y:=(1-s)*y1+s*y2:

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

> plot3d([x,y,z],s=0..1,t=0..6*Pi,scaling=constrained,grid=[5,100],
title="87121 By J.S.C.");