如何证明coq中的〜（all a，〜（P a））->（exists a，P a）？

Question

Coq convert non exist to forall statement显示了另一个问题，但是与我无法申请的方式非常相关。

我怎么证明

Lemma ee' : forall (T : Type) (P : T->Prop), ~(exists a, ~(P a)) -> (forall a, P a).

其他版本的证明

WITH 
dates AS ( SELECT test.Date FROM test 
           UNION
           SELECT test2.Date FROM test2 ),
total AS ( SELECT *
           FROM dates
           LEFT JOIN test USING(Date) 
           UNION ALL
           SELECT *
           FROM dates
           LEFT JOIN test2 USING(Date) )
SELECT total.Date, SUM(USD) USD, SUM(EUR) EUR
FROM total
GROUP BY total.Date
ORDER BY total.Date;

也很感激。