From Chesspedia, the Free Chess Encyclopedia.
Diemer-Duhm Gambit
| 8 |  |
 |
 |
 |
 |
 |
 |
 |
| 7 |  |
 |
|
 |
 |
|
|
|
| 6 | |
|
|
|
|
|
|
|
| 5 | |
|
|
|
|
|
|
|
| 4 | |
|
 |
 |
|
|
|
|
| 3 | |
|
|
|
|
|
|
|
| 2 | |
|
|
|
|
|
|
|
| 1 |  |
 |
 |
 |
 |
 |
 |
 |
| a | b | c | d | e | f | g | h |
The Diemer-Duhm Gambit (DDG) is a chess opening that begins either with
- 1. e4 e6 2. d4 d5 3. c4 (via French Defense) or
- 1. d4 d5 2. c4 e6 3. e4 (via Queen's Gambit Declined).
The Gambit is accepted if black plays 3...dxe4. After that the main line is 4. Nc3 Nf6 5. f3, though there are many variations. After 5. f3 the Gambit splits into three main lines, the Kmoch Variation, the Keres Variation, and the Exchange variation, which are 5...Bb4, 5...c5, and 5...exf3 respectively.
The name of the opening comes from the German master Emil Joseph Diemer, father of Blackmar-Diemer Gambit.
No books have been written about the DDG, but games, analysis and articles are found on the DDG site.
In short, the DDG is a dubious opening, but fun to play.