Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...Nf6/4. Ng5/4...d5/5. exd5/5...Na5/6. Bb5/6...c6/7. dxc6/7...bxc6/8. Qf3/8...Rb8/9. Bd3

Two Knights:Colman Defence
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) 1rbqkb1r/p4ppp/2p2n2/n3p1N1/8/3B1Q2/PPPP1PPP/RNB1K2R b
Moves: 1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. Ng5 d5 5. exd5 Na5 6. Bb5 c6 7. dxc6 bxc6 8. Qf3 Rb8 9. Bd3

Two Knights:Colman Defence

9. Bd3

This bishop retreat, while unnatural due to it blocking in the d-pawn, gives added protection of the e4 square, which White's knight may soon occupy. This makes this a tough move for Black to face.

Theory table

.

1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 d5 5.exd5 Na5
6.Bb5+ c6 7. dxc6 bxc6 8. Qf3 Rb8 9.Bd3

	9	10	11	12	13
1	Bd3 Be7	O-O O-O	Re1 Rb4	Nc3 Rf4	∞
2	... h6	Ne4 Nd5	b3 g6	Qg3	+=
3	... Bd6	Nc3 O-O	+=
4	... Rb4	Nc3 Be7	+=

References

Wikipedia has related information at Two Knights Defence.

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Chess Opening Theory

1. e4 e5
Open games

2. Nf3

2...Nc6

3. Bb5
Spanish

• Berlin →
  • Anti-Berlin
  • Beverwijk
  • L'Hermet → Berlin Wall

• Morphy →
  • Exchange
  • Closed →
    • Marshall
    • Chigorin
    • Flohr
  • Open
  • Arkhangelsk
  • Anderssen
  • Mackenzie

• Bird
• Classical
• Cozio
• Old Steinitz
• Schliemann

3. Bc4
Italian

• Giuoco Piano →
  • Evans gambit
  • Giuoco pianissimo
  • Rosentreter
  • Jerome ??

• Two knights defence →
  • Open
  • Knight attack →
    • Fried liver
    • Polerio

• Anti-fried liver ?!
• Blackburne shilling ?

3. Nc3
Three knights

• Four knights →
  • Glek
  • Italian
  • Scotch → Belgrade
  • Spanish
  • Naroditsky !?
  • Halloween ?!

• Steinitz
• Schlechter

Other

• Ponziani
• Scotch game
• Konstantinopolsky !?

2...Nf6
Russian

• Classical
• Kholmov
• Modern
• Boden-Kieseritzky !?
• Stafford ?
• Damiano trap ??

2...d6
Philidor

• Exchange
• Philidor countergambit
• Nimzowitsch
• Hanham

Other

• Busch-Gass gambit ?
• Elephant gambit ?
• Greco defence ?!
• Latvian gambit ?
• Damiano defence ??

2. f4
King's gambit

2...exf4
Accepted

• King's knight →
  • Kieseritzky
  • Schallop
  • Modern
  • Fischer
  • Lolli ?
  • Muzio ?
• Bishop's →
  • Cozio

Other
Declined

• Classical
• Queen's knight
• Falkbeer

2. Nc3
Vienna

• Falkbeer →
  • Mieses
  • Stanley
  • Frankenstein-Dracula
  • Vienna gambit
• Max Lange

Other

• Bishop's opening →
  • Berlin
  • Boi
• Centre game →
  • Danish
• Leonardis
• Parham ?!
• Portuguese ?!
• Bongcloud ?

1. e4 c5
Sicilian

2. Nf3

2...Nc6 3. d4 cxd4 4. Nxd4

• Accelerated dragon →
  • Maróczy bind
• Classical
• Godiva
• Kalashnikov
• Sveshnikov

2...Nc6 other

• Rossolimo
• Delayed Alapin

2...d6 3. d4 cxd4 4. Nxd4

• Dragon →
  • Levenfish attack
  • Yugoslav attack
• Dragondorf
• Kupreichik
• Najdorf →
  • 6. Bg5
  • English attack
  • Opocensky
• Scheveningen

2...d6 other

• Moscow
• Chekhover
• Delayed Alapin

2...e6 3. d4 cxd4 4. Nxd4

• French, Normal
  • American attack
  • Four knights
  • Pin
• Kan
• Kveinis
• Paulsen-Basman
• Taimanov →
  • Bastrikov →
    • English attack
  • Szén →
    • Garry Gambit

2...e6 other

• Kramnik
• Delayed Alapin

Others

• Hyper-accelerated dragon
• Katalymov
• Nimzowitsch
• O'Kelly

Anti-Sicilians

• Alapin
• Bowdler
• Closed Sicilian →
  • Carlsen
  • Grand Prix
  • Fianchetto
• McDonnell
• Mengarini
• Smith-Morra
• Snyder
• Staunton-Cochrane
• Wing gambit

1. e4 e6
French

• Advance
• Classical
• Exchange
• Tarrasch
• Rubinstein
• Winawer

1. e4 c6
Caro-Kann

• Classical
• Advance →
  • Short
  • van der Wiel
• Exchange
• Panov-Botvinnik Attack
• Accelerated Panov
• Two Knights
• Fantasy
• Hillbilly ?!

1. e4 other

• Alekhine
• Czech
• Modern
• Nimzowitsch
• Owen's
• Pirc →
  • Lion
  • Austrian
  • 150
• Scandinavian →
  • Classical
  • Modern
  • Blackburne-Kloosterbooer gambit !?
  • Tennison gambit ?!

• Barnes ?
• Borg ?
• Corn stalk ??
• Duras ??
• 1...b5 ??

1. d4 d5
Closed games

2. c4
Queen's gambit

• Albin countergambit
• Austrian
• Chigorin
• Marshall
• Queen's gambit accepted
• Queen's gambit declined
• Slav →
  • Semi-Slav

2. Nc3

• Richter-Versov
• Irish gambit
• Jobava London

2. other

• Accelerated London
• Colle
• Levitsky !?
• Amazon ?!
• Blackmar-Diemer ?
• Mason ?
• Zurich ??

1. d4 Nf6
Indian

2. c4 e6

• Bogo-Indian
• Catalan
• Nimzo-Indian
• Queen's Indian
• Seirawan
• Devin gambit !?

2. c4 g6

• King's Indian →
  • Classical
  • Four pawns attack
  • Sämisch
• Grünfeld

2. c4 other

• Accelerated queen's Indian
• Modern Benoni →
  • Benko
• Budapest
• Mexican
• Old Indian

2. Nf3

• Spielmann Indian
• Torre

2. other:

• Trompowsky →
  • Edge
  • Raptor
• London system (Indian)
• Paleface ?!
• Bronstein gambit !?
• Omega ?

1. d4 f5
Dutch

• Hopton
• Korchnoi
• Leningrad
• Staunton
• Stonewall →
  • Bladel

1. d4 ...other:

• English defence
• Australian defence ?!
• Englund gambit ?
• Horwitz
• Old Benoni
• Polish
• Rat

1. Nf3
Zukertort

• Réti
• King's Indian defence (d5)
• King's Indian defence (Nf6)
• Lisitsin gambit !?
• Lemberger gambit ?
• Ross gambit ?
• Herrstrom gambit ?

Flank

• Bird's (1. f4)
• English (1. c4)
• Grob (1. g4)
• King's fianchetto (1.g3)
• Larsen (1. b3)

Unorthodox

• a3
• Na3
• a4
• b4
• c3
• Nc3
• d3
• e3
• f3
• h3
• Nh3
• h4