Darboux surfaces

wreath of

Surfaces associated with an infinitesimal deformation of one of them; discovered by G. Darboux [1]. Darboux surfaces form a "wreath" of 12 surfaces, with radius vectors $ \mathbf x _ {1} \dots \mathbf x _ {6} , \mathbf z _ {1} \dots \mathbf z _ {6} $ satisfying the equations

$$ d \mathbf z _ {i} = [ \mathbf z _ {i + 1 } , d \mathbf x _ {i} ] ,\ \ d \mathbf x _ {i} = [ \mathbf x _ {i - 1 } , d \mathbf z _ {i} ] , $$

$$ \mathbf z _ {i} - \mathbf x _ {i + 1 } = [ \mathbf z _ {i+ 1 } , \mathbf x _ {i} ],\ i = 1 \dots 6 , $$

$$ \mathbf x _ {i + 6 } = \mathbf x _ {i} ,\ \mathbf z _ {i + 6 } = \mathbf z _ {i} ; $$

where $ \mathbf z _ {i+} 1 $ and $ \mathbf x _ {i} $ are in Peterson correspondence, $ \mathbf z _ {i+} 1 $ and $ \mathbf x _ {i-} 1 $ are in polar correspondence, while $ \mathbf z _ {i} $ and $ \mathbf x _ {i+} 1 $ are poles of a $ W $- congruence. A similar "wreath" is formed by pairs of isometric surfaces of an elliptic space.

#### References[edit]

[1] |  G. Darboux, "Leçons sur la théorie générale des surfaces et ses applications géométriques du calcul infinitésimal" , 4 , Gauthier-Villars (1896)

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[2] |  V.I. Shulikovskii, "Classical differential geometry in a tensor setting" , Moscow (1963) (In Russian)

#### Comments[edit]

For the notion of a $ W $- congruence cf. Congruence of lines.

#### References[edit]

[a1] |  G. Fubini, E. Čech, "Introduction á la géométrie projective différentielle des surfaces" , Gauthier-Villars (1931)

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[a2] |  G. Bol, "Projective Differentialgeometrie" , Vandenhoeck & Ruprecht (1954)