ONLY IF


Meaning of ONLY IF in English

(rather formal ) used to state the only situation in which sth can happen :

Only if a teacher has given permission is a student allowed to leave the room.

Only if the red light comes on is there any danger to employees.

Oxford Advanced Learner's English Dictionary.      Оксфордский английский словарь для изучающик язык на продвинутом уровне.