Calculate the average number of female students who are disabled and who joined Foreign Legion organization.
average = DIVIDE(COUNT(disabled.name who are not in male.name WHERE organ = 'foreign_legion'), COUNT(disabled.name)); female students who are disabled refers to disabled.name who are NOT in male.name; organization refers to organ; organ = 'Foreign Legion';
SELECT CAST(SUM(IIF(T3.name IS NULL, 1, 0)) AS REAL) / COUNT(T1.name) FROM disabled AS T1 INNER JOIN enlist AS T2 ON T1.name = T2.name LEFT JOIN male AS T3 ON T2.name = T3.name WHERE T2.organ = 'foreign_legion'