SELECT - parenthesis ignored by Oracle ???

I do
select distinct(year || period)
from IC_BIN_MOVEMENTS
WHERE WAREHOUSE='SF'
AND (PERIOD<>10 AND YEAR<>2001);

That is, I want all rows where warehouse = SF and the date is not october 2001.
What it returns is all rows for warehouse SF where the period is not 10 (of any year) and year is not 2001.
As a result I get all months except october for every year, and nothing at all for the whole year 2001.

Why are the parenthesis ignored?

Thanks! Received on Fri Dec 14 2001 - 10:51:48 CST