Neat! I've not seen anything quite like this before. The first thing after a non-quoted list is not interpreted as a function.
> (setq a '((1 2) 3))
((1 2) 3)
> (a 1)
3
>
Thyping (a 1 2) is as easy to type as a[1][2] and maybe as easy to read?
Eddie
... and it also works with indices in vectors (forgot to mention this in the changes notes, but its in the manual):
(set 'L '(a b (c d (e f) g)))
(L 2 2 0 ) => e
(set 'vec '(2 2 0))
(L vec) => e
This way 'push', 'pop' and 'ref' fit all together with implicit indexing
Lutz