Removing simliar elements from a set

Hi folks,

I'm trying to remove items from a set which are similar to items in
another set.

This is the set (MASTER) from which I wish to remove items:

/ports/Mk/bsd.python.mk
/ports/lang/python-doc-html/distinfo
/ports/lang/python/Makefile
/ports/lang/python/distinfo
/ports/lang/python/files/patch-Modules-Setup.dist

These are the items (MATCHES) which are the prefixes which must be
removed:

/ports/lang/python-doc-html
/ports/lang/python

In this case, the answer would be:

/ports/Mk/bsd.python.mk

In short, we remove all items from MASTER which are under the directories
specified in MATCHES.

My first attempt, which works only if MATCHES contains one item:

SELECT *
FROM MASTER JOIN MATCHES
ON NOT (MASTER.pathname ~ ('^' || MATCHES.pathname || '/.+'));

However, if there is more than one row in MATCHES, this will not work.

Clues please?
--
Dan Langille - http://www.langille.org/