The "Encyclopedia of Chess Openings" ("ECO") classifies all King's Pawn Games into volumes B or C: volume C if the game starts with (the French Defence) or ; volume B if Black answers with any other move. The rare instances where the opening does not fall into a more specific category than "King's Pawn Game" are included in codes B00 (includes the Nimzowitsch Defence and unusual moves after 1.e4), C20 (includes Alapin's Opening and unusual moves after 1.e4 e5), C40 (includes the Latvian Gambit and unusual moves after 1.e4 e5 2.Nf3), and C50 (includes the Hungarian Defence, the Giuoco Pianissimo, and unusual moves after 1.e4 e5 2.Nf3 Nc6 3.Bc4).