Describe how two pipes of the same size are joined perpendicularly.

> restart;

> x:=cos(t):

> y:=sin(t):

> z1:=-1.5:

> z2:=x:

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

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

> b:=reflect(a,[[0,0,0],[1,0,1],[2,-1,2]]):

> with(plottools):

> display(a,b);

>