The revenue equivalence theorem states that, if all bidders are risk-neutral bidder and have independent private value for the auctioned items, then all four of the standard single unit auctions have the same expected sales price (or seller's revenue).The four standard single unit auctions are the English auction, the Dutch auction, first-price sealed-bid auction, and the second-price sealed-bid auction.
Given the preconditions, how is it possible for an English auction to genereate the same revenue as a first-price sealed auction?
Per my understanding, an English auction, when played optimally, generates the same revenue as a second price sealed auction (Vickrey auction).
On the other hand, a First Price Sealed Bid, when played optimally, results in a revenue equivalent to the highest bid.
So how can the two be revenue equivalent?