C42 Petrov’s Defense
C42 holds 40 named lines, all under the name Petrov’s Defense. It leaves C40 (King’s Knight Opening) with 2...Nf6. Material is no longer level at the end of 13 of its lines; the widest gap, two pawns in White’s favour, comes in Petrov’s Defense: Cochrane Gambit. After 2...Nf6 the position is a mirror image: every Black man stands opposite its White counterpart.
| # | White | Black |
|---|---|---|
| 1 | e4 | e5 |
| 2 | Nf3 | Nf6 |
The move that completes C42
The reference line of C43 plays all of these moves and continues beyond them; C42 is the position reached at 2...Nf6.
- 2...Nf6 The knight leaves g8 for f6, opening a line for the rook on h8.
Lines filed under C42
All 40 share their first four plies, the whole reference line and then split four ways at White’s move 3.
| Name | After the shared start | Plies | At the end |
|---|---|---|---|
| Petrov’s Defense | (the shared start itself) | 4 | |
| Petrov’s Defense | 3.Nxe5 | 5 | White +1 |
| Petrov’s Defense: Italian Variation | 3.Bc4 | 5 | |
| Petrov’s Defense: Three Knights Game | 3.Nc3 | 5 | |
| Petrov’s Defense | 3.Nxe5 d6 | 6 | White +1 |
| Petrov’s Defense: Damiano Variation | 3.Nxe5 Nxe4 | 6 | |
| Petrov’s Defense: Stafford Gambit | 3.Nxe5 Nc6 | 6 | White +1 |
| Petrov’s Defense | 3.Nxe5 d6 4.Nf3 | 7 | White +1 |
| Petrov’s Defense: Cochrane Gambit | 3.Nxe5 d6 4.Nxf7 | 7 | White +2 |
| Petrov’s Defense: Karklins-Martinovsky Variation | 3.Nxe5 d6 4.Nd3 | 7 | White +1 |
| Petrov’s Defense: Moody Gambit | 3.Qe2 Nc6 4.d4 | 7 | |
| Petrov’s Defense: Paulsen Attack | 3.Nxe5 d6 4.Nc4 | 7 | White +1 |
| Petrov’s Defense | 3.Nxe5 d6 4.Nf3 Nxe4 | 8 | |
| Petrov’s Defense: Damiano Variation, Kholmov Gambit | 3.Nxe5 Nxe4 4.Qe2 Qe7 | 8 | |
| Petrov’s Defense: Stafford Gambit Accepted | 3.Nxe5 Nc6 4.Nxc6 dxc6 | 8 | White +1 |
| Petrov’s Defense: Classical Attack | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 | 9 | |
| Petrov’s Defense: Cochrane Gambit, Bishop Check Line | 3.Nxe5 d6 4.Nxf7 Kxf7 5.Bc4+ | 9 | Black +1, check |
| Petrov’s Defense: Cochrane Gambit, Center Variation | 3.Nxe5 d6 4.Nxf7 Kxf7 5.d4 | 9 | Black +1 |
| Petrov’s Defense: Cozio Attack | 3.Nxe5 d6 4.Nf3 Nxe4 5.Qe2 | 9 | |
| Petrov’s Defense: French Attack | 3.Nxe5 d6 4.Nf3 Nxe4 5.d3 | 9 | |
| Petrov’s Defense: Kaufmann Attack | 3.Nxe5 d6 4.Nf3 Nxe4 5.c4 | 9 | |
| Petrov’s Defense: Millennium Attack | 3.Nxe5 d6 4.Nf3 Nxe4 5.Bd3 | 9 | |
| Petrov’s Defense: Nimzowitsch Attack | 3.Nxe5 d6 4.Nf3 Nxe4 5.Nc3 | 9 | |
| Petrov’s Defense: Classical Attack, Closed Variation | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 Nf6 | 10 | |
| Petrov’s Defense: Stafford Gambit Accepted | 3.Nxe5 Nc6 4.Nxc6 dxc6 5.Nc3 Bc5 | 10 | White +1 |
| Petrov’s Defense: Stafford Gambit Accepted | 3.Nxe5 Nc6 4.Nxc6 dxc6 5.d3 Bc5 | 10 | White +1 |
| Petrov’s Defense: Classical Attack, Marshall Variation | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Bd6 | 12 | |
| Petrov’s Defense: Classical Attack, Mason-Showalter Variation | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Nc6 | 12 | |
| Petrov’s Defense: Classical Attack, Mason Variation | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Be7 7.O-O O-O | 14 | both castled |
| Petrov’s Defense: Classical Attack, Chigorin Variation | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Be7 7.O-O Nc6 8.Re1 | 15 | White castled |
| Petrov’s Defense: Classical Attack, Jaenisch Variation | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Nc6 7.O-O Be7 8.c4 | 15 | White castled |
| Petrov’s Defense: Classical Attack, Staunton Variation | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Bd6 7.O-O O-O 8.c4 c6 | 16 | both castled |
| Petrov’s Defense: Classical Attack, Tarrasch Variation | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Bd6 7.O-O O-O 8.c4 Bg4 | 16 | both castled |
| Petrov’s Defense: Classical Attack, Chigorin Variation, Browne Attack | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Nc6 7.O-O Be7 8.c4 Nb4 9.cxd5 | 17 | White +1, White castled |
| Petrov’s Defense: Classical Attack, Chigorin Variation, Main Line | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Nc6 7.O-O Be7 8.c4 Nb4 9.Be2 | 17 | White castled |
| Petrov’s Defense: Classical Attack, Marshall Variation, Chinese Gambit | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Bd6 7.O-O O-O 8.c4 c6 9.Re1 Bg4 | 18 | both castled |
| Petrov’s Defense: Classical Attack, Berger Variation | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Be7 7.O-O Nc6 8.Re1 Bg4 9.c3 f5 10.Nbd2 | 19 | White castled |
| Petrov’s Defense: Classical Attack, Krause Variation | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Nc6 7.O-O Be7 8.Re1 Bg4 9.c3 f5 10.c4 | 19 | White castled |
| Petrov’s Defense: Classical Attack, Marshall Trap | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Bd6 7.O-O O-O 8.c4 Bg4 9.cxd5 f5 10.Re1 Bxh2+ | 20 | both castled, check |
| Petrov’s Defense: Classical Attack, Maróczy Variation | 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Be7 7.O-O Nc6 8.Re1 Bg4 9.c3 f5 10.c4 Bh4 | 20 | White castled |
The road to C42
- 1.e4one earlier stop: B00
- 1...e5C20 King’s Pawn Game
- 2.Nf3C40 King’s Knight Opening
- 2...Nf6C42
The position after 2...Nf6
White has brought out the knight on f3; Black the knight on f6. White could capture with Nxe5. Undefended and attacked: the pawn on e5. White is to move and has 27 legal moves.
Codes that branch off from C42
The reference lines of one other code leave C42 from the position after 2...Nf6, each with its own moves.
| Code | Moves | Reference line |
|---|---|---|
| C43 | 3.d4 | Petrov’s Defense: Modern Attack |
Closest boards in other codes
| Code | Line | Differs on |
|---|---|---|
| A05 | Zukertort Opening | four squares: e2, e4, e5, e7 |
| B02 | Alekhine Defense | four squares: g1, f3, e5, e7 |
| B29 | Sicilian Defense: Nimzowitsch Variation | four squares: c5, e5, c7, e7 |
| C20 | King’s Pawn Game | four squares: g1, f3, f6, g8 |
| C24 | Bishop’s Opening: Berlin Defense | four squares: f1, g1, f3, c4 |
| C26 | Vienna Game: Falkbeer Variation | four squares: b1, g1, c3, f3 |
| C41 | Philidor Defense | four squares: d6, f6, d7, g8 |
Where lines continue from here
Sixteen named lines filed under other codes pass through the position after 2...Nf6. Besides the codes above, they belong to C27, C48, C49.