OpenLLM-France/wikimedia huggingface dataset:
# Sicilian - O'Kelly variation
### 2...a6

This early a6 prevents White from occupying b5, so after 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 e5 and then 6. Nb5 is prevented. The main problem with this variation is how to deal with 3. c3, which transposes to an Alapin Sicilian with the useless a6 move. Another problem is 3. c4 d6 d4 Bg4 dxc5 Bxf3 gxf3! dxc5 (An alternative is Qa5+ Nc3 Qxc5 (dxc5?! Qb3 (Ra7!?) Qc7? (Black would have done better to give up a pawn) Bf4! with a winning attack) Be3 Qc6 with a huge lead in development and two Bishops). Qxd8+ Kxd8. For the ruined structure, white has a crushing attack and 2 Bishops. d4 is also absolutely normal move

## Theory table

For explanation of notation, see Chess Opening Theory Table.
1.e4 c5 2.Nf3 a6
| 3 | 4 | 5 |
| c3 d5 | exd5 Nf6 | c4 e6 | += |
| Nc3 e6 | d4 cxd4 | Nxd4 | See Kan Sicilian |
| d4 cxd4 | Nxd4 e5 | Ne2 Bc5 | = |
| ... ... | Qxd4!? Nc6 | |
| c4 e6 | Nc3 Qc7 | Be2 b6 | = |
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## References

* Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.
# Open Sicilian

Black's 2...d6 gives them the option of several popular attacking lines, controls the e5 square, supports the c-pawn and activates their queen's bishop.
White's rationale for playing 2. Nf3 was to support a 3. d4 advance which they may now play. Their best alternative to this, for rapid development, is 3. Bb5+, forcing Black to block the check with a minor piece that would then be pinned to the king. Swashbuckling players might be tempted by 3. b4, planning an unopposed d4 when the Black c-pawn is diverted to b4.

## Theory table

For explanation of theory tables, see theory table and for notation, see algebraic notation.
1. e4 c5 2. Nf3 d6
| | 3 | 4 | 5 | 6 |
| Main line | d4 cxd4 | Nxd4 Nf6 | Nc3 a6 | Be3 e6 | = |
| Moscow Variation (or Canal-Sokolsky Attack) | Bb5+ Bd7 | Bxd7+ Qxd7 | O-O Nc6 | c3 Nf6 | = |
| | Nc3 Nf6 | e5 dxe5 | Nxe5 Nbd7 | Nc4 e6 | +/= |
| Delayed Alapin | c3 Nf6 | Be2 g6 | O-O Bg7 | Bb5+ Nbd7 | = |
| Deferred Wing Gambit | b4 cxb4 | d4 Nf6 | Bd3 e6 | O-O Be7 | =/+ |
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## References

* Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.
* Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.
# Sicilian Defence, Maroczy Bind

Moves:1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 g6 5.c4 Bg7 6.Be3 Nf6 7.Nc3
    7...Ng4: Breyer Variation
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## References

* This Chess related article is a stub. Please assist Wikibooks by expanding it.
# Maroczy Bind, Breyer Variation

Moves:1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 g6 5.c4 Bg7 6.Be3 Nf6 7.Nc3 Ng4
This opening is ECO code B39.

## Theory table

| 8 | 9 | 10 | 11 |
| Qxg4 Nxd4 | Qd1 Ne6 | - - | - - | 0.33 |
| ... Bxd4 | Bxd4 Nxd4 | O-O-O d6 | - - | 0.40 |
| ... ... | ... ... | Bd3 d5 | - - | 0.04 |
| ... ... | Qe2 O-O | - - | - - | -0.01 |
| Nxc6 Nxe3 | - - | - - | - - | -0.04 |
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# Sicilian - Nimzowitsch Variation
### 2...Nf6

This attack on the e4 pawn is similar to the Alekhine's Defence. White normally plays e5 to attack the knight on f6.

## Theory table

For explanation of notation, see Chess Opening Theory Table.
1.e4 c5 2.Nf3 Nf6
| 3 | 4 | 5 |
| e5 Nd5 | Nc3 e6 | Nxd5 exd5 | += |
| Nc3 d6 | | | See 2... d6 |
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## References

* Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.
* This Chess related article is a stub. Please assist Wikibooks by expanding it.
# Open Sicilian
### 3...e6
## Theory table

For explanation of theory tables, see theory table and for notation, see algebraic notation. .
1.e4 c5 2.Nf3 Nc6 3.d4 e6
| | 4 | 5 |
| Sicilian, Taimanov | Nc3 cxd4 | to 3.Nc3 e6 4.d4 |
| | c3 | to 3.c3 e6 4.d4 |
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# Sicilian - O'Kelly variation - Venice System ("Enhanced" Alapin)
### 3. c3

The only line for black that even approaches equality (by winning percentage) is 3. ... e6. In every other line it seems white has a much easier time of it, with win percentages approaching double that of black. This can be referred an "enhanced" Alapin based on white getting an extra developed Knight due to black's essentially wasted a6.

## Theory table

1.e4 c5 2.Nf3 a6 3.c3
| 3 | 4 | 5 |
| ... d5 | exd5 Qxd5 | d4 e6 | += |
| ... d5 | exd5 Nf6 | c4 e6 | += |
| ... e6 | d4 d5 | e5 Bd7 | = |
When contributing to this Wikibook, please follow the Conventions for organization.

## References

* Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.
# Sicilian, Canal-Sokolsky (Rossolimo) Attack
### 3...Bd7
## Theory table

For explanation of theory tables, see theory table and for notation, see algebraic notation. .
1.e4 c5 2.Nf3 d6 3.Bb5+ Bd7
| | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
| Sicilian, Canal-Sokolsky (Rossolimo) Attack | Bxd7+ Qxd7 | |
| | a4 Nc6 | |
| | c4 a6 | Bxd7+ Nxd7 | d4 cxd4 | Nxd4 Ngf6 | Nc3 g6 | 0-0 Bg7 | Qf3 0-0 | Be3 Ne5 | Qe2 Ngf4 | Bf4 Nf6 | b3 Nh5? | b3 += |
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# 20th Century

1900-1920
http://www.fashion-era.com/images/Edwds1890-1915/tailorhatsmarbx20.jpg Beginning of 20th century
http://www.fashion-era.com/images/Edwds1890-1915/gibsonmarbx30.jpg Typical "Gibson" girl
https://archive.is/20130703235031/www.costumes.org/travel/usitt2001/6/Mvc-013f.jpg 1904
https://archive.is/20130704002217/www.costumes.org/travel/usitt2001/6/Mvc-020f.jpg 1909
http://upload.wikimedia.org/wikipedia/commons/7/75/Molly_brown_rescue_award_titanic.jpg Molly Brown, 1912
1920s
Influence of cinema, Hollywood, and the "celebrity" were greatly apparent.
http://www.fashion-era.com/images/1914-1950/1920lines.jpg 1920
https://archive.is/20130703232728/www.costumes.org/history/20thcent/1920s/fashionplates/1920tailleur2.JPG
http://www.fashion-era.com/images/1914-1950/jagg400.jpg 1925
http://www.fashion-era.com/images/1914-1950/1920chemiscorsb.jpg 20s undergarments
http://www.fashion-era.com/images/1914-1950/eton500.jpg Popular 20s hairstyles
http://www.artdesignfashion.com/timelines/images/1920s.jpg
http://www.fashion-era.com/images/1920s_photos/flappers_duo.jpg Flappers
1930s
http://www.fashion-era.com/images/1920s_photos/october1930hilda500.jpg Wedding party, 1930
http://thinkinpictures.files.wordpress.com/2007/06/g-chanel-by-manrayl.jpg
http://www.fashionmuseum.co.uk/userImages/virtualTour/moc5v.jpg Evening wear
http://i211.photobucket.com/albums/bb241/fashionising/keira-knightley-atonement.jpg Atonement
http://www.dargate.com/255_auction/255_images/1170.jpg
https://archive.is/20130703235635/www.costumes.org/history/20thcent/1930s/sears/spring1934cottondresses2.JPG 1934 Women's ready-made frocks
1940s - 1950
# Costume History

Welcome to the Costume History wikibook, a British and Western-centred textbook which examines the history of clothing from Ancient Egypt to the 20th Century. This is a free textbook that anyone can edit, so feel free to contribute!

## Chapters

* Egyptian
* Greek
* Roman
* Byzantine
* Medieval
* Renaissance
* Elizabethan
* Charles and the Commonwealth
* Restoration
* Georgian
* Romantic
* Crinoline
* Bustle
* Victorian
* 20th Century
* Indian

## See also

* Corset
# Crinoline

I. History A. 1840~1865 (ish) B. II. Men A. Hair Curly hair was the most popular. Fixed in many ways it was mostly slicked with perfumed macassar oil. Sideburns were still popular. The stovepipe top hat was in fashion for formal occasions while the short wide brimmed hat was worn for sport and outings. Neck wear ranged from bow ties, long ties, and cravats to string ties, ascots, and stocks. B. Bodies Tail coats and frock coats were popular during this time. For casual wear sack coats were worn. The collars diminished greatly in height from the thirties. Shoulders dropped to elongate the neck. Sleeves were kept tight. C. Legs Long tubular pants were the fashion for men. Shoes were kept small and unassuming. III. Women A. Hair Hair was kept close to the nape of the neck and in large masses. Women either wore bonnets or pinned small hats on their heads if they wore them at all. B. Bodies Neck lines varied a lot but generally stayed bellow the pit of the throat. The sloping shoulder was emphasized and the women’s figure emphasized to look especially feminine. Shawls became the outer garment of choice. C. Legs The crinoline period is so called for use of crinoline in making women’s skirts puff out. Crinoline is a fabric made of a mixture of horse hair (crin) and linen (lin). This fabric was used to make petticoats. Eventually so many layers were used that it was impossible to use more when W.S. Thomas perfected David Hough’s invention of the hoop skirt. People continued incorrectly to call the crinolines but they causing skirts to continue to travel outward. Causing women to look like bells. Slippers were fashionable for indoors well ankle boots were fashionable for street ware. Flats were fashionable at the beginning and heels came into fashion slowly.
Materials General clothing • Muslin • Lawn • Tarlatan • Gingham • Calico • Percale • Dimity • Merino • Grenadine • Flannel • Serge • Broadcloth Fancy clothing • Silk • Taffeta • Crepe • Brocade • Velvet • Grosgrain • Satin • Moiré Antique
Colors Men • Generally bright colors were avoided Women • Nothing was unused
Jewelry Men wore rings and cuff links. The also wore shirt studs. Women wore cameos, necklaces, earrings, bracelets, and large broaches. Lockets were also popular. semiprecious stones like turquoise and garnet were popular along with pearls.
# Dichotomous Key/Perissodactyla

* Parent key: Mammalia
* Subclasses
* Marsupialia - Monotremata - Placentalia
* Key: Mammalia
* Orders
* Afrosoricida - Artiodactyla - Carnivora - Cetacea - Chiroptera - Dermoptera - Insectivora - Lagomorpha - Macroselidae - Marsupialia - Monotremata - Perissodactyla - Pholidota - Primates - Proboscidea - Rodentia - Scandentia - Sirenia - Xenarthra

## 1

* Number of toes
** One - #2: Equidae
** More - #3

## 3

* Horn
** Present - #4: Rhinocerotidae
** Not present - #5: Tapiridae

## #4: Rhinocerotidae

* Number of horns
** One - Rhinoceros sondaicus
** Two - Either Diceros bicornis or Dicerorhinus sumatrensis
# Dichotomous Key/Passeriformes

* Aves keys
* Orders
* Accipitriformes | Anseriformes | Apodiformes | Caprimulgiformes | Charadriiformes | Dichotomous Key/Ciconiiformes | Coliformes | Columbiformes | Coraciiformes | Cuculiformes | Falconiformes | Galliformes | Gaviiformes | Gruiformes | Passeriformes | Pelecaniformes | Podicipediformes | Procellariiformes | Psittaciformes | Pterocliformes | Sphenisciformes | Dichotomous Key/Strigiformes | Struthioniformes | Dichotomous Key/Tinamiformes | Trochiliformes | Trogoniformes | Turniciformes

## 1

* Syrinx complexity
** Very complex - #2: Passeri
** Simple - #3: Tyranni

## 2: Passeri

* Number of fossa
** One - #4: Corvida
** Two - #5: Passerida

## 4: Corvida

* Mimicking behavior
** Yes - #6: Menuridae
** No - #7: Corvida

## 7: Corvida

* Tongue texture
** Brush tipped, bristly - #8 - Meliphagidae
** Smooth, or other - #9 - Corvida

## 9 - Corvida

Could be Atrichornithidae, Climacteridae, Maluridae, Pardalotidae, Petroicidae, Pomatostomidae, Cinclosomatidae, Neosittidae, Pachycephalidae, Dicruridae, Campephagidae, Oriolidae, Artamidae, Paradisaeidae, Corvidae, Corcorachidae, Irenidae, Laniidae, Vireonidae, Ptilonorhynchidae
# Dichotomous Key/Placentalia

* Parent key: Mammalia
* Subclasses
* Marsupialia - Monotremata - Placentalia
* Key: Mammalia
* Orders
* Afrosoricida - Artiodactyla - Carnivora - Cetacea - Chiroptera - Dermoptera - Insectivora - Lagomorpha - Macroselidae - Perissodactyla - Pholidota - Primates - Proboscidea - Rodentia - Scandentia - Sirenia - Xenarthra

## 1

* Pulp cavity
** Not present (thin tubes of dentine instead) - Orycteropus afer
** Present - 2
| Dentine: | The substance between the enamel (crown) or cementum (root) of a tooth and the pulp chamber. |

## 2

* Limbs
** Adapted for flight or gliding - 3
** Adapted for land movement or swimming - 4

## 3

* Capability of true flight
** Yes - Chiroptera
** No - Dermoptera

## 4

* Limbs adapted for swimming
** Yes - 5
** No - 6

## 5

* Legs
** Present or vestigial - #16
** Absent - Sirenia

## 6

* Number of fingers
** Five - Primates
** Other amounts or none - 7

## 7

* Hooves
** Present - 10
** Not present - 8

## 8

* Trunk presence
** Yes - Proboscidea
** No - 9

## 9

* Incisors
** Developed, located at the front of the jaw - 12
** Undeveloped, side teeth used for grazing - 11

## 10

* Number of toes
** Any odd number - Perissodactyla
** Any even number - Artiodactyla

## 11

* Teeth growth
** Throughout lifetime - 12
** Only during maturation - 13

## 12

* Number of incisors in upper jaw
** Four - Lagomorpha
** Two - Rodentia

## 13

* Presence of bony scales
** Yes - 14
** No - 15

## 14

Could be of the order Pholidota or an armadillo (family Dasyopodidae)

## 15

* Dentition
** Prominent canines and carnassials - Carnivora
** Other - 16

## 16

* Legs
** Vestigial - Cetacea
** Present - #17

## 17

Could be of the orders Afrosoricida, Macroscelidea, Xenarthra, Scandentia, Insectivora, Cetacea
# Dichotomous Key/Pinophyta

1: Trees or erect or ascending shrubs, 1 meter or more high.
    2: Extant (not extinct)...........................................................................Pinales
    2: Produces cones or arils.....................................................................Pinales
    2: Late Carboniferous, Dutch-Belgian-German Coal area; long, strap-shaped
    leaves (up to 80 cm in length), parallel venation; grew in coastal environments as
    swamp plants and in cool temperate forests of Angaraland.......................Cordaitales
# Dichotomous Key/Orthoptera
## 1

* Antennae, tarsi, ovipositor
** Antennae much shorter than body. Tarsi 2-3 segmented. Ovipositor short and composed of 2 pairs of short, horny, diverging plates - 2: Caelifera
** Antennae as long as or longer than the body. Tarsi 3-4 segmented. Ovipositor elongate and either swordshaped or cylindrical - 3: Ensifera
# Dichotomous Key/Petromyzonidae

Dichotomous Key: Petromyzonidae :
* Kingdom: Animalia
* Phylum: Animalia
* Subphylum: Chordata
* Class: Petromyzonidae
Information related to Petromyzonidae :
* Wikipedia
* Wikispecies
* Wikicommons
* Parent key: Chordata
* Subphyla
* Vertebrata
* Key: Petromyzonidae
* Vertebrata
* Clerck, 1757
Glossary for this page (all links are to Wikipedia articles) :
* Dorsal fin:
* Caudal fin:
* Chordata keys
* Subphyla
* Myxini | Urochordata
* Classes
* Actinistia | Actinopterygii | Amphibia | Aves | Chondrichthyes | Dipnoi | Mammalia | Petromyzontida | Reptilia
This is a Dichotomous Key for the Family Petromyzonidae.

## 1

* Dorsal and caudal fin distinction
** The dorsal and caudal fins are distinct - Dichotomous Key:Petromyzon
** The dorsal and caudal fins are not distinct - #2

## 2

* Depth of dorsal fin notch
** Shallow - Dichotomous Key:Ichthyomyzon
** Deep - Dichotomous Key:Lampetra
# Dichotomous Key/Phoenicopteridae
## Key to the species of Phoenicopteridae

* 1: Legs are either grayish or yellow
* 2: Legs are clearly red or pink

## 1

* Phoenicopterus andinus: Eyes are dark red-brown; Legs are yellow.
* Phoenicopterus chilensis: Eyes are pale yellow; Legs are greyish with a pink joint.

## 2

* Phoenicopterus ruber: Plumage is a deep pink to red color.
* 3: Plumage is mostly a light pink color

## 3

* Phoenicopterus jamesi: Beak is yellow with a black tip.
* 4: Beak is not yellow

## 4

* Phoenicopterus roseus: Large in size; Height is over 100 centimeters
* Phoenicopterus minor: Small in size; Height is under 100 centimeters
# Dichotomous Key/Pinaceae

1: Pinaceae
    2: Cones biennial, rarely triennial, with each year's scale growth distinct, forming an umbo on
    each scale. Cone scale base broad, concealing the seeds fully from abaxial view. Seed without
    resin vesicles. Seed wing holding the seed in a pair of claws. Leaves with primary stomatal
    bands adaxial (above the xylem) or equally on both surfaces.......................................................Pinus
    2: Cones annual, without a distinct umbo. Cone scale base broad, concealing the seeds
    fully from abaxial view. Seed without resin vesicles, blackish. Seed wing holding the seed
    loosely in a cup. Leaves with primary stomatal bands adaxial (above the xylem) or equally on
    both surfaces.........................................................................................................................Picea
    2: Cones annual, without a distinct umbo. Cone scale base broad, concealing the seeds fully
    from abaxial view. Seed without resin vesicles, whitish. Seed wing holding the seed tightly in a
    cup. Leaves with primary stomatal bands abaxial (below the phloem vessels) only........Subfamily Laricoideae
    2: Cones annual, without a distinct umbo. Cone scale base narrow, with the seeds partly visible
    in abaxial view. Seed with resin vesicles. Seed wing holding the seed tightly in a cup. Leaves
    with primary stomatal bands abaxial (below the phloem vessels) only..........................Subfamily Abietoideae
# Dichotomous Key/Pinales

The order Pinales is composed of
* Pinaceae
* Araucariaceae
* Podocarpaceae
* Sciadopityaceae
* Cupressaceae
* Cephalotaxaceae
* Taxaceae
* Phyllocladaceae
* †Emporiaceae
* †Majonicaceae
* †Ullmanniaceae
* †Utrechtiaceae
* †Voltziaceae
Incertae sedis
   * †Paahake
1: Trees produce cones or arils.
    2: Leaves alternate or in fascicles or clusters (not opposite or whorled), needle-like,
    (scale-like leaves often present on fruiting branches of Taxodium); fruit a cone.
       3: Leaves in fascicles of 2-5 leaves or mostly in clusters of many leaves on
       spur-like branches.
          4: Leaves in fascicles of 2-5 leaves, persistent.........................Pinus
          4: Leaves mostly in clusters of many leaves on the ends of spur-like branches,
          deciduous............................................................................Larix
       3: Leaves scattered, alternate.
          5: Ultimate twigs very slender, greenish and mostly deciduous; leaves deciduous, yellowish-green,
          much flattened and in two ranks; bark fibrous; cones with several wedge-shaped
          woody scales......................................................................Taxodium
          5: Ultimate twigs not deciduous; leaves persistent, not yellowish-green above;
          bark not fibrous.
             6: Branchlets roughened by the persistent leaf bases; leaves deciduous when dry; cones pendulous, the bracts shorter than the cone scales.
                7: Leaves sessile, mostly four-sided, often sharp-pointed................Picea
                7: Leaves stalked, flattened, blunt......................................Tsuga
             6: Branchlets not roughened by persistent leaf bases.
                8: Leaves sessile, flattened, (seldom four-sided); leaf-scars orbicular, not decurrent;
                cones erect, the scales deciduous.......................................Abies
                8: Leaves stalked, flattened; leaf-scars decurrent.
                   9: Leaves mostly with obtuse tips and with two white lines on the lower surface;
                   cones pendulous, the scales persistent in the axils of long exserted bracts.........Pseudotsuga
                   9: Leaves with acute tips, yellow-green on the lower surface; "fruit" drupe-like........Taxus
    2: Leaves opposite or whorled, often of two kinds, scale-like, awl-shaped, or linear.
# Dichotomous Key/Parasitiformes
## 1

* Latigynial plates and palpal tarsus
** Both reduced - 2
** Neither reduced - 3

## 2: Ixodida

* Attachment to host
** Remain attached for long periods - Ixodidae
** Do not remain attached long - Argasidae
Could also be the poorly-known Nuttalliellidae

## 3

* Diet
** Scavenger - Holothyrida
** Other - Mesostigmata
# Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...Nf6/4. Ng5/4...Bc5/5. d4/5...d5
## Theory table

For explanation of theory tables, see theory table and for notation, see algebraic notation. .
    1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Bc5 5. d4 d5
| | 5 | 6 | 7 |
| 1 | ... d5 | Bxd5 Nxd5 | dxc5 Nb4 |
| 2 | ... ... | Bxd5 Nxd4 | Bxf7 Ke7 | ∞ |
When contributing to this Wikibook, please follow the Conventions for organization.
# Two Knights Defence
### 4...Nxe4?

Not the best move for Black. Ignoring the threat of White's position, they grab the e-pawn. This initially seems like a good move because Black has 5...d5 after 5. Nxe4? forking the knight and bishop.
However, White can now capture Black's unprotected f-pawn with check: 5. Bxf7+ Ke7 6. d4! and Black cannot yet take on g5 without losing his queen.
5. Nxf7 is a mistake, as after 5... Qh4 Black gains an advantage even against White's best defense.

## Theory table

For explanation of theory tables, see theory table and for notation, see algebraic notation.
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Nxe4
| 5 | 6 | 7 |
| Bxf7+ Ke7 | d4 d5 | Nc3 | += |
| | ... Nxd4 | Nc3 Nf6 | += |
| | ... h6 | Nxe4 | += |

## References

* Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.
* Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.
# Two Knights Defence
### 5. Bxf7+

White correctly captures with the bishop, putting Black in check. With Black given no chance at counterplay, White now has a long-term goal of attacking with their queen and minor pieces on the kingside.

## Theory table

For explanation of theory tables, see theory table and for notation, see algebraic notation.
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Nxe4 5. Bxf7+
| 5 | 6 | 7 |
| Bxf7+ Ke7 | d4 d5 | Nc3 | += |
| | ... Nxd4 | Nc3 Nf6 | += |
| | ... h6 | Nxe4 Kxe7 | += |

## References

* Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.
* Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.
# Two Knights Defence
### 5... Ke7

In this position, White must make one more critical move to retain their advantage. If Black manages to trade knights with 6...Nxg5, Black will be able to stabilize their position.
The move 6. d4! prevents this as 6...Nxg5 7. Bxg5 skewers the king and queen. Black capturing the d-pawn is now the least of their worries as White can begin to mount a powerful offensive.

## Theory table

For explanation of theory tables, see theory table and for notation, see algebraic notation.
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Nxe4 5. Bxf7+ Ke7
| 6 | 7 | 8 |
| h6 Nxe4 | Kxf7 d5 | Nd4 c3 | += |

## References

* Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.
* Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.
# Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...Nf6/4. Ng5/4...Bc5/5. d4
## 5. d4!?

Rather than capturing the undefended f-pawn, White plays it safe and attacks the bishop while preventing the idea of Bxf2+.
Moving away the bishop is a mistake because after Nxf7, White captures a free rook and Black has no counterplay without the bishop sacrifice.
Capturing the d-pawn with the pawn or knight will similarly prevent the bishop sacrifice.
Another mistake is if Black captures with the bishop (5...Bxd4) and goes for the sacrifice anyway (6. Nxf7 Bxf2+). The difference between this position and if 5. d4 Bxd4 was never played is that White's queen and dark-squared bishop can protect key squares from Black's fierce counterattack.
Therefore, Black's only sensible move here is 5...d5, stopping a capture on f7.
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