Merging 2 stacks ?

[Richmond Mathewson]

  Is it possible to merge 2 main stacks;

So, for the sake of argument; cards 1, 2, 3 & 4 of
one stack can become cards 1, 2, 3 & 4 of another
stack, and cards 1, 2, 3 & 4 of that one become
cards 5, 6 ,7 & 8?