The obligations of a dealer (including an underwriter no longer acting as an underwriter in respect of the security involved in such transactions) to deliver a prospectus in transactions in a security as to which a registration statement has been filed taking place prior to the expiration of the 40- or 90-day period specified in section 4(3) of the Act after the effective date of such registration statement or prior to the expiration of such period after the first date upon which the security was