Question: Southeastern Airlines was acquired by a carrier of what regional airline that operates short and medium-haul routes?

full_context: Document 1: Mainline (aeronautics): A mainline flight is a flight operated by an airline's main operating unit, rather than by regional alliances, regional code-shares, regional subsidiaries, or wholly owned subsidiaries offering low-cost operations. Mainline carriers typically operate between hub airports within their network and on international or long-haul services, using narrow-body and wide-body aircraft. This is in contrast to regional airlines, providing feeder services to hub airports operating smaller turboprop or regional jet aircraft, or low-cost carrier subsidiaries serving leisure markets.
Document 2: American Eagle (airline brand): American Eagle is an American brand name for the regional branch of American Airlines, under which ten individual regional airlines operate short- and medium-haul feeder flights. Three of these airlines, Envoy Air (formerly American Eagle Airlines), Piedmont Airlines and PSA Airlines, are wholly owned subsidiaries of American Airlines Group. Just like the regional brands of the other two major airlines (Delta Connection and United Express), American Airlines' regional brand accounts for more than 60% of American Airlines flights.
Document 3: Delta Connection: Delta Connection is a regional airline brand name for Delta Air Lines, under which a number of individually owned regional airlines operate short- and medium-haul routes. Delta's lone wholly owned regional airline, Endeavor Air, also resides under the Delta Connection banner. Mainline carriers often use regional airlines to operate services in order to increase frequency, serve routes that would not sustain larger aircraft, or for other competitive reasons.
Document 4: Mesaba Airlines: Mesaba Aviation, Inc. (operating as Mesaba Airlines) was an American regional airline based in Eagan, Minnesota The airline was a wholly owned subsidiary of Pinnacle Airlines Corporation. Its flights operated as Delta Connection for Delta Air Lines and US Airways Express for US Airways. Previously, the airline operated as Northwest Airlink and Northwest Jetlink on behalf of Northwest Airlines which subsequently merged with Delta. Mesaba Airlines effectively ceased operations on January 4, 2012, when all aircraft and personnel were transitioned to the Pinnacle Airlines operating certificate. Mesaba's operating certificate was surrendered on July 31, 2012.
Document 5: Atlantic Southeast Airlines: Atlantic Southeast Airlines (ASA) was an American airline based in the A-Tech Center in College Park, Georgia, flying to 144 destinations as a Delta Connection carrier and, as of February 2010, commenced service as a United Express carrier. It was a wholly owned subsidiary of SkyWest, Inc. ASA operated nearly 900 flights each day. Its main hub was at Hartsfield-Jackson Atlanta International Airport (ATL). ASA changed its name to ExpressJet in 2011.
Document 6: SkyWest Airlines: SkyWest Airlines is a North American airline owned by SkyWest, Inc. and headquartered in St. George, Utah, U.S.. According to the Airlines for America definitions, SkyWest is a North American major airline. SkyWest however, operates on a regional airline level and is a member of the Regional Airline Association. SkyWest Airlines flies to 238 cities, in 45 states; Washington, D.C., six Canadian provinces and five cities in Mexico. The airline serves as a feeder airline, operating under contract with various major carriers. It flies as SkyWest Airlines in a partnership with Alaska Airlines, as United Express on behalf of United Airlines, as American Eagle on behalf of American Airlines, and as Delta Connection on behalf of Delta Air Lines. SkyWest also provides ground handling services for airports across the United States.
Document 7: Eastern Air Lines Shuttle: Eastern Air Lines Shuttle (or Eastern Air Shuttle) was the brand name of Eastern's air shuttle. It began operations on April 30, 1961 and was sold in 1989 to Donald Trump, and later became the Trump Shuttle. In April 1992, the shuttle service began as the USAir Shuttle (presently American Airlines Shuttle). The shuttle originally flew between New York City, Boston, Washington, D.C. and Newark. The shuttle's slogan was "Imagine life without us."
Document 8: Atlantic Gulf Airlines: Atlantic Gulf Airlines was a regional airline founded by Tom Tepper and Kerry Broaddus in Florida that began operations in October 1983. Service started with two British-manufactured Vickers Viscount four engine turboprop airliners. Atlantic Gulf was one of very few airlines in the U.S. to operate the Viscount in scheduled passenger service (Continental Airlines and United Airlines operated Viscounts during the 1960s as did Aloha Airlines and Hawaiian Airlines). The airline began with service from Miami to St. Petersburg, Florida. By early 1984, the airlines had added Convair 580 turboprops to the fleet and was operating Miami (MIA) - St. Petersburg (PIE) - Atlanta (ATL) service. The fleet grew to three Convair 580s and cities such as Tallahassee and Fort Lauderdale were added to the route system.
Document 9: US Airways Express: US Airways Express was the brand name for the regional affiliate of US Airways, under which a number of individually owned commuter air carriers and regional airlines operate short and medium haul routes. This code sharing service was previously operated as USAir Express. Mainline carriers often outsource to regional airlines to operate services in order to increase frequency, serve routes that would not sustain larger aircraft, or for other competitive reasons. US Airways Express operations were conducted from smaller markets in the United States, Canada, and the Bahamas primarily centered on US Airways' major hubs and focus cities. Upon the completion of US Airways' merger process with American Airlines, US Airways Express was rebranded as American Eagle on October 17, 2015.
Document 10: Northwest Airlink: Northwest Airlink was the trade name of Northwest Airlines' regional airline service, which flew turboprop and regional jet aircraft from Northwest's domestic hubs in Minneapolis, Detroit, and Memphis. Service was primarily to small-to-medium-sized cities and towns where larger aircraft might not be economical to operate and also to larger markets to either provide additional capacity or more frequent flights than could be justified using mainline aircraft. Beginning in July 2009, the Northwest Airlink trade name was phased out, and replaced by the Delta Connection trade name for Delta Air Lines as part of the Delta/Northwest merger.
Document 11: Northeast Express Regional Airlines: Northeast Express Regional Airlines was a regional airline based in Manchester, New Hampshire. The airline was originally known as Valley Airlines started by Maine businessman Roland Martin it capitalized on the US government essential air service by flying intrastate Maine to small communities that otherwise would not have access to airline services. Then the airline was brought by Allen Caruso of Bar Harbor Airlines fame. They rebranded and became Northeast Express Regional Airlines and became a Northwest Airlines codeshare affiliate dba Northwest Airlink. The airline declared bankruptcy and was liquidated, along with its sister company Precision Airlines, in 1995.
Document 12: Southeastern Airlines: Southeastern Airlines was a regional airline that was acquired by Atlantic Southeast Airlines, a Delta Connection carrier, on April 1, 1983. It was formed in 1982 by Atlanta entrepreneur Michael J. Brady, who had formerly been head of Eastern Metro Express, a feeder for Eastern Airlines.
Document 13: Air Southwest: Air Southwest was a British airline founded by Sutton Harbour Holdings in 2003. Ownership was transferred to Eastern Airways in September 2010 but operations ceased 12 months later. It operated regional scheduled passenger services in the South West of England. Its main base was Plymouth City Airport, with hubs at Newquay Cornwall Airport and Bristol Airport. The airline employed 145 people and was headed by managing director Peter Davies and Deputy chief executive Mike Coombes.
Document 14: Business Express Airlines: Business Express Airlines (IATA: HQ) , often referred to as Business Express or BizEX, was an American regional airline founded as Atlantic Air in 1982. In an effort to appeal to its predominantly business commuter clientele, the airline assumed the Business Express name in 1985. In 1986 Pilgrim Airlines (Groton/New London), which itself had acquired NewAir (New Haven) about a year prior, was acquired by the airline. This opened the valuable New York and Washington, D.C. markets. Shortly thereafter, Business Express became one of Delta Air Lines's first Delta Connection carriers, along with Atlantic Southeast Airlines, Comair and SkyWest Airlines.
Document 15: Delta Air Lines: Delta Air Lines, Inc. ("Delta"; ) is a major American airline, with its headquarters and largest hub at Hartsfield–Jackson Atlanta International Airport in Atlanta, Georgia. The airline along with its subsidiaries and regional affiliates operate over 5,400 flights daily and serve an extensive domestic and international network that includes 319 destinations in 54 countries on six continents, as of October 2016. Delta is one of the four founding members of the SkyTeam airline alliance, and operates joint ventures with Air France-KLM, Alitalia, Korean Air, China Eastern Airlines, Virgin Atlantic, and Virgin Australia. Regional service is operated under the brand name Delta Connection.
ground_truth: Delta Connection