Also, DL used to have roundtrip D1 fares on JFK-LAX (requiring staying until at least first Saturday after departure). These started at $1300 each-way for Z fares vs. $1500 for one-way Z fares. Roundtrip fares have an 'F' in second letter of fare basis code vs. an 'A' for one-ways. They ditched the roundtrip fare filings back in October when they bumped one-way fares up to $1600.