two table comparison: find a mismatch?

Hello,

here is to table:
Table "city"
Attribute | Type | Modifier
----------------+-------------+---------------------------------------------
city_id | smallint | not null default
nextval('seq_city'::text)
region_id | smallint |
region_tour_id | smallint |
country_id | smallint |
name_fr | varchar(40) |
name | varchar(40) |
url_id | smallint |

Table "region"
Attribute | Type | Modifier
-----------+-------------+----------------------------------------------
region_id | smallint | not null default nextval('seq_region'::text)
country_id| smallint |
name_fr | varchar(40) |
name | varchar(40) |
address | boolean |
url_id | smallint |

I whant to fins a "hole" in the linkage... a region number in the city
table is not in the region table any more.

How can I do that?

Where is the city.region_id <> region.region_id

Thanks!
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Marc Andre Paquin