How to make a "side-window", in an arbitrary configuration?

[martin rudalics]

> Here is the most simple case: suppose I have a window configuration like this:
>
> -----
> | | |
> |a|b|
> | | |
> -----
>
> How do I convert it to this?
>
> -----
> |a|b|
> -----
> | c |
> -----

With Emacs >= 24.1 do either

(split-window (frame-root-window))

or

(split-window (window-parent))

martin