NEW YORK CITY? Hilton Hotels and Promus Hotel Corp. hammered out a definitive merger agreement whereby Beverly Hills-based Hilton will acquire Memphis-based Promus in a cash-and-stock transaction valued at some $4 billion. The deal was announced at the Waldorf=Astoria here on Sept. 7. With pieces of the deal falling into place quicker than many industry observers believed they might (even faster than principals of the two lodging companies had reason to expect), the addition of Promus to the Hilton Hotels fold will result in one of the world?s largest and most diverse lodging entities, with more than 1,700 hotels.