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There is an approach to intersection number, introduced by Snapper in 1959-60 and developed later by Cartier and Kleiman, that defines an intersection number as an Euler characteristic. Let X be a scheme over a scheme S , Pic( X ) the Picard group of X and G the Grothendieck group of the category of coherent sheaves on X whose support is proper ...
As well as being called the intersection number, the minimum number of these cliques has been called the R-content, [7] edge clique cover number, [4] or clique cover number. [8] The problem of computing the intersection number has been called the intersection number problem , [ 9 ] the intersection graph basis problem , [ 10 ] covering by ...
As another example, the number 5 is not contained in the intersection of the set of prime numbers {2, 3, 5, 7, 11, …} and the set of even numbers {2, 4, 6, 8, 10, …} , because although 5 is a prime number, it is not even. In fact, the number 2 is the only number in the intersection of these two
A key example of self-intersection numbers is the exceptional curve of a blow-up, which is a central operation in birational geometry. Given an algebraic surface S, blowing up at a point creates a curve C. This curve C is recognisable by its genus, which is 0, and its self-intersection number, which is −1. (This is not obvious.)
K) is a Chern number and the self-intersection number of the canonical class K, and e = c 2 is the topological Euler characteristic. It can be used to replace the term χ(0) in the Riemann–Roch theorem with topological terms; this gives the Hirzebruch–Riemann–Roch theorem for surfaces.
One way to classify intersections is by the number of road segments (arms) that are involved. A three-way intersection is a junction between three road segments (arms): a T junction when two arms form one road, or a Y junction, the latter also known as a fork if approached from the stem of the Y.
Equivalently, D is nef if the intersection number is nonnegative for every curve C in X. To go back from line bundles to divisors, the first Chern class is the isomorphism from the Picard group of line bundles on a variety X to the group of Cartier divisors modulo linear equivalence.
There will be an intersection if 0 ≤ t ≤ 1 and 0 ≤ u ≤ 1. The intersection point falls within the first line segment if 0 ≤ t ≤ 1, and it falls within the second line segment if 0 ≤ u ≤ 1. These inequalities can be tested without the need for division, allowing rapid determination of the existence of any line segment ...