Chess Opening Theory/1. d4/1...d5/2. e4/2...dxe4/3. Nc3/3...e5

= Blackmar-Diemer Gambit (BDG): Lemberger Countergambit=

3... e5
Black has advanced their pawn to e5 and offers a pawn transfer. If White takes the e5 pawn, then Qxd1 forces White to either give up the right to castle with Kxd1 or undevelop the knight with Nxd1. However, there are better options such as Nxe4, encouraging Black to take d4 with the queen and make a queen trade, or Nge2, declining the countergambit and protecting the d4 pawn.

Traps
The Sneiders attack with Qh5 can lead to a winning position on the 6th move with Nd5?!, with most opponents going Qd7? and blundering Qe5+! and Nxc7!. However, there are players who refute this with a counterattack of their own with Nf6, leading to a queen exchange with both knights capturing the opposing queens.

Theory table
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'''1. d4 d5 2. e4 dxe4 3. Nc3 e5'''