orientable
51Poincaré duality — In mathematics, the Poincaré duality theorem, named after Henri Poincaré, is a basic result on the structure of the homology and cohomology groups of manifolds. It states that if M is an n dimensional compact oriented manifold, then the k th… …
52Dehn twist — A positive Dehn twist applied to a cylinder about the red curve c modifies the green curve as shown. In geometric topology, a branch of mathematics, a Dehn twist is a certain type of self homeomorphism of a surface (two dimensional manifold).… …
53Reduction of the structure group — In mathematics, in particular the theory of principal bundles, one can ask if a G bundle comes from a subgroup H < G. This is called reduction of the structure group (to H), and makes sense for any map H o G, which need not be an inclusion… …
54Heawood conjecture — The Heawood conjecture or Ringel–Youngs theorem in graph theory gives an upper bound for the number of colors which are sufficient for graph coloring on a surface of a given genus. It was proven in 1968 by Gerhard Ringel and J. W. T. Youngs. One… …
55Weeks manifold — In mathematics, the Weeks manifold, sometimes called the Fomenko Matveev Weeks manifold, is a closed hyperbolic 3 manifold obtained by (5,2) and (5,1) Dehn surgeries on the Whitehead link. It has volume approximately equal to .9427... and has the …
56Graph embedding — In topological graph theory, an embedding of a graph G on a surface Sigma; is a representation of G on Sigma; in which points of Sigma; are associated to vertices and simple arcs (homeomorphic images of [0,1] ) are associated to edges in such a… …
57Differential geometry of surfaces — Carl Friedrich Gauss in 1828 In mathematics, the differential geometry of surfaces deals with smooth surfaces with various additional structures, most often, a Riemannian metric. Surfaces have been extensively studied from various perspectives:… …
58Alunisseur — Module lunaire Apollo Pour les articles homonymes, voir LEM et LM. Module lunaire du programme Apollo …
59Lunar Module — Module lunaire Apollo Pour les articles homonymes, voir LEM et LM. Module lunaire du programme Apollo …
60Module Lunaire — Apollo Pour les articles homonymes, voir LEM et LM. Module lunaire du programme Apollo …
