instruction: what was the top four of the most frequent procedures?
response: SELECT d_icd_procedures.short_title FROM d_icd_procedures WHERE d_icd_procedures.icd9_code IN (SELECT t1.icd9_code FROM (SELECT procedures_icd.icd9_code, DENSE_RANK() OVER (ORDER BY COUNT(*) DESC) AS c1 FROM procedures_icd GROUP BY procedures_icd.icd9_code) AS t1 WHERE t1.c1 <= 4)