SELECT without pair (B,A) if I have (A, B)

Here is a simple question, when I have (A,B) as a result of my query, I would like to have only (A,B), not (B,A).

For exemple my query retus :

161, 52 
161, 53
53, 161
53, 161

Here is my query :

SELECT S1.SURVEY_ID, S2.SURVEY_ID

  FROM SURVEYS S1, SURVEYS S2

  WHERE (S2.START_DATE BETWEEN S1.START_DATE and S1.END_DATE
  OR S2.END_DATE BETWEEN S1.START_DATE and S1.END_DATE)
  AND S1.SURVEY_ID != S2.SURVEY_ID

ORDER BY S1.SURVEY_ID, S2.SURVEY_ID