emacs lisp: make list of lists into one list

[oaul]

Hello, how the F do you combine lists of lists:

((1 2 3) (4 5 6) (7 8 9))

into this:
(1 2 3 4 5 6 9 8 9)

[oaul]

I ALWAYS do this on this forum. You use append. Still learning...