Try This
       --------

In the Test program

  - insert cat then dog
  - toggle
  - insert fox
  - append
  - show
  - insert yak
  - show 

Explain what you see.

Now do the following

   - remove yak
   - show

Explain what you see.

Now do the following
   
   - remove cat
   - show

Explain again what you see.


Patrick