Getting points from polygon - Mailing list pgsql-sql

Hello,

how can I get single xy-points from a polygon like for example:

CREATE TABLE "public"."country" 
("country_id" INTEGER NOT NULL,    "geo" polygon NOT NULL    
)

SELECT geo.x, geo.y FROM country WHERE geo.x=5

or

SELECT geo[24th point].x FROM country

...

Thanks in advance and best regards,
Sebastian