Chess Opening Theory/1. d4/1...d5/2. c4/2...e6/3. Nc3/3...c6/4. Nf3

Triangle system
	a b c d e f g h 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 a b c d e f g h
	Position in Forsyth-Edwards Notation (FEN) rnbqkbnr/pp3ppp/2p1p3/3p4/2PP4/2N2N2/PP2PPPP/R1BQKB1R
	Moves: 1. d4 d5 2. c4 e6 3. Nc3 c6 4. Nf3
	ECO code: D31
	Parent: Triangle system

4. Nf3

White develops the knight and leaves the opening choice to Black. The move 4...Nf6 transposes into the Semi-Slav defence, while 4...dxc4 enters the sharp Noteboom variation.

Theory table

1. d4 d5 2. c4 e6 3. Nc3 c6 4. Nf3

	4
Semi-Slav defence	... Nf6	=
Noteboom variation	... dxc4	∞

References

Wikipedia has related information at Semi-Slav Defence.

Triangle system
a b c d e f g h 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 a b c d e f g h
Position in Forsyth-Edwards Notation (FEN) rnbqkbnr/pp3ppp/2p1p3/3p4/2PP4/2N2N2/PP2PPPP/R1BQKB1R
Moves: 1. d4 d5 2. c4 e6 3. Nc3 c6 4. Nf3
ECO code: D31
Parent: Triangle system