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What (who) is null tetrad - definition

IRREDUCIBLE NODAL SURFACE

Kummer's surface; Rosenheim tetrad; Gopel tetrad; Göpel tetrad

Construction of a complex null tetrad

PAIR OF REAL NULL VECTORS AND A PAIR OF COMPLEX NULL VECTORS

Wikipedia talk:Articles for creation/Construction of a complex null tetrad

Calculations in the Newman–Penrose (NP) formalism of general relativity normally begin with the construction of a complex null tetrad \{l^a,n^a,m^a,\bar{m}^a\}, where \{l^a,n^a\} is a pair of real null vectors and \{m^a,\bar{m}^a\} is a pair of complex null vectors. These tetrad vectors respect the following normalization and metric conditions assuming the spacetime signature (-,+,+,+):

https://en.wikipedia.org/wiki/Construction_of_a_complex_null_tetrad

Null allele

NONFUNCTIONAL ALLELE (A VARIANT OF A GENE) CAUSED BY A GENETIC MUTATION

Null mutation; Null Allele; Null alleles; Null mutant

A null allele is a nonfunctional allele (a variant of a gene) caused by a genetic mutation. Such mutations can cause a complete lack of production of the associated gene product or a product that does not function properly; in either case, the allele may be considered nonfunctional.

https://en.wikipedia.org/wiki/Null_allele

Null (SQL)

SPECIAL MARKER AND KEYWORD IN SQL INDICATING THAT SOMETHING HAS NO VALUE

Sql null; NULL (SQL); NVL; NULLIF; SQL CASE; Sql case; Codd tables; Codd table; COALESCE; C-table; Uncertain database; NULL marks; Null (database)

In SQL, null or NULL is a special marker used to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E.

https://en.wikipedia.org/wiki/Null_(SQL)

Wikipedia

Kummer surface

In algebraic geometry, a Kummer quartic surface, first studied by Ernst Kummer (1864), is an irreducible nodal surface of degree 4 in $\mathbb {P} ^{3}$ with the maximal possible number of 16 double points. Any such surface is the Kummer variety of the Jacobian variety of a smooth hyperelliptic curve of genus 2; i.e. a quotient of the Jacobian by the Kummer involution x ↦ −x. The Kummer involution has 16 fixed points: the 16 2-torsion point of the Jacobian, and they are the 16 singular points of the quartic surface. Resolving the 16 double points of the quotient of a (possibly nonalgebraic) torus by the Kummer involution gives a K3 surface with 16 disjoint rational curves; these K3 surfaces are also sometimes called Kummer surfaces.

Other surfaces closely related to Kummer surfaces include Weddle surfaces, wave surfaces, and tetrahedroids.

https://en.wikipedia.org/wiki/Kummer surface