Blackmar-Diemer Gambit Declined: Vienna Defense

The Blackmar-Diemer Gambit Declined: Vienna Defense is a chess opening classified under ECO code D00 in the Closed & Semi-Closed Games family, arising from 1.d4 d5, including the Queen's Gambit, Slav Defense, and related systems. It is reached after 4 moves: 1. d4 d5 2. e4 dxe4 3. Nc3 Nf6 4. f3 Bf5. The resulting position leaves white to move.