Lesson
White to move. Main line: 1. d4 d5 2. c4 e5 3. dxe5 d4 4. e3 Bb4+ 5. Bd2 dxe3 6. Bxb4 exf2+ 7. Ke2 fxg1=N+ 8. Rxg1 Bg4+
The natural 4.e3? runs into 4...Bb4+ 5.Bd2 dxe3, and after 6.Bxb4 exf2+ 7.Ke2 the pawn on f2 promotes — but 7...fxg1=N+! is the star move. A new queen would allow Rxh8; the knight promotion comes with check, and after 8.Rxg1 Bg4+ Black regains the queen with a winning position.
This is the classic reason underpromotion exists: sometimes a knight’s check beats a queen’s power. The 3.dxe5 d4 wedge is the whole point of the Albin — it cramps White and sets exactly these traps.