Subquery in INSERT?

What I'm trying to do is copy a value from one column to another in the same
table. The table looks like this:

first | second
---------------------
1 |
2 |
3 |
4 |
...

It's named 'copier'.

The first column is sequence-generated, and the second has yet to have
anything loaded (at this stage it's only a test table). So what I'm trying
to do is quick copy of '1' from 'first' to 'second' with this query:

INSERT INTO copier VALUES(nextval('sequence'), ((SELECT first FROM copier
WHERE copier.first=1) AS second));

...and I'm getting this error:
ERROR: syntax error at or near "AS" at character 93

So what I want to know is, is it possible? If it is and my query is
incorrect and anyone can tell me what's wrong with it that would be great.

Thanks a lot.

-Wilf.

P.S. Sorry if I posted this twice.

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