Need help with attributes...

I created a latitude/longitude function (it's Richard Lynch's, actually) that returns the distance between to points.  What I don't know how to do is use this value as a filter in the select statement:

PostgreSQL Error: 1 (ERROR: Attribute 'distance' not found )
select distinct zip_code, gpsdistance(34.2865, 118.435, latitude, longitude) as distance from zipcodes where distance
<= 10.0

The value for distance is actually available, however:
 

select distinct zip_code, gpsdistance(34.2865, 118.435, latitude, longitude) as distance from zipcodes where zip_code
like '913%'

91301 16.3049416821461,
91302 12.858968990111,
91303 8.71667347958831,
91304 8.67013652211651,
91305 8.45399567001425,
91306 .....

Any assistance on this question of syntax would be gratefully accepted

-- 
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Scott Holmes                       http://www.pacificnet.net/~sholmes
                                   sholmes@pacificnet.net

  Independent Programmer/Analyst                  Passport 4GL        
  HTML Composer                                   Informix 4GL, SQL
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