[postgis-devel] How do you obtain the line that touches a polygon?

[googling1000]

Hi,
I have one polygon, and a line lies exactly on an edge of that polygon.
How do I obtain that line?

Please take a look at a picture here:
http://googling1000.googlepages.com/example.jpg
(I drew the lines using different thickness so it is easy to understand
where each segment ended)
The line segment A is touching the polygon P, and I'd like to write a query
statement that will fetch me that line.

I tried ST_intersects and ST_Touches, but the queries return 0 rows.

Then, I tried && which is another intersection command?
This is the query statment:
select ST_AsText(myline.the_geom) from myline,mypoly where mypoly.the_geom
&& myline.the_geom AND mypoly.polynum = '11'
Note that 11 is the number associated with polygon P

I was hoping to get only the A segment, but I got all A,B,C segments as a
result. why is that?
How do I obtain segment A?

Help will be highly appreciated.
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