Database: thrombosis_prediction
Question: Among the patients who has a normal anti-scl70, how many of them are female and does not have any symptom?
SQL: SELECT COUNT(DISTINCT T1.ID) FROM Patient AS T1 INNER JOIN Laboratory AS T2 ON T1.ID = T2.ID INNER JOIN Examination AS T3 ON T3.ID = T2.ID WHERE (T2.SC170 = 'negative' OR T2.SC170 = '0') AND T1.SEX = 'F' AND T3.Symptoms IS NULL