From an ordinary card deck with 52 cards, we select n cards successively. We consider the events A1: the first card drawn is an ace;

An: in the first n − 1 selections (n ≥ 2), neither an ace nor a face card is drawn and in the nth selection an ace is drawn, where n = 2, 3,… Write down an expression, in terms of A1, A2,…, for the event that an ace is drawn before a face card.