ECO C31: King's Gambit Declined & Van Geet Opening

ECO C31 is part of volume C, Open Games. The Lichess chess-openings dataset files 15 named lines under it, from 2 different openings. The shortest is King's Gambit Declined: Falkbeer Countergambit: 1. e4 e5 2. f4 d5.

That position has come up in 6,178,512 Lichess games between players rated 1600 to 2500: White won 46.7%, 3.9% were drawn and Black won 49.3%.