The following SQL statement:
SELECT TD_WEDNESDAY(TIMESTAMP'2012-05-08 10:00:00+01:00','ISO');
returns 2012-05-02 01:00:00+01:00.
The following SQL statement:
SELECT TD_WEDNESDAY(TIMESTAMP'2012-05-08 10:00:00+01:00','ISO');
returns 2012-05-02 01:00:00+01:00.