An aftermarket for a single brand can be a viable product market but only when 1) the challenged aftermarket restrictions are “not generally known” when consumers make their foremarket purchase; (2) “significant” information costs prevent accurate life-cycle pricing; (3) “significant” monetary or non-monetary switching costs exist; and (4) general market-definition principles regarding cross-elasticity of demand do not undermine the proposed single-brand market. Here, plaintiff failed to establish that the applications-market for Apple iPhones was a separate single brand aftermarket. The district court erred in holding that an antitrust market can never relate to a product that the defendant does not license or sell because the defendant might profit from the product in other ways. Lack of consumer knowledge, however, must be shown. One way of doing so is by showing that the defendant adopted its restrictive policy only after a substantial number of consumers purchased its product, but lack of consumer knowledge can also be shown by other means. Here, the district court’s finding that Epic had not proven lack of consumer knowledge of Apple’s policy of requiring app developers to use the Apple App Store and pay Apple 30% of their gross revenues from app store sales. That failure doomed Epic’s antitrust claims for lack of proof of a product market.