zbMATH — the first resource for mathematics

Examples
Geometry Search for the term Geometry in any field. Queries are case-independent.
Funct* Wildcard queries are specified by * (e.g. functions, functorial, etc.). Otherwise the search is exact.
"Topological group" Phrases (multi-words) should be set in "straight quotation marks".
au: Bourbaki & ti: Algebra Search for author and title. The and-operator & is default and can be omitted.
Chebyshev | Tschebyscheff The or-operator | allows to search for Chebyshev or Tschebyscheff.
"Quasi* map*" py: 1989 The resulting documents have publication year 1989.
so: Eur* J* Mat* Soc* cc: 14 Search for publications in a particular source with a Mathematics Subject Classification code (cc) in 14.
"Partial diff* eq*" ! elliptic The not-operator ! eliminates all results containing the word elliptic.
dt: b & au: Hilbert The document type is set to books; alternatively: j for journal articles, a for book articles.
py: 2000-2015 cc: (94A | 11T) Number ranges are accepted. Terms can be grouped within (parentheses).
la: chinese Find documents in a given language. ISO 639-1 language codes can also be used.

Operators
a & b logic and
a | b logic or
!ab logic not
abc* right wildcard
"ab c" phrase
(ab c) parentheses
Fields
any anywhere an internal document identifier
au author, editor ai internal author identifier
ti title la language
so source ab review, abstract
py publication year rv reviewer
cc MSC code ut uncontrolled term
dt document type (j: journal article; b: book; a: book article)
Counting symmetric configurations v 3 . (English) Zbl 0940.05020

An incidence geometry (P,) consists of a set of v points P={p 1 ,,p v } and a collection of b blocks ={B 1 ,,B b } such that B i P for i=1,2,,b. The number of blocks containing a point pP is called the degree, denoted by [p]. Blocks are also called lines and |B| is called the length of the block B. A pair (p,B) with pB is called a flag. In this case, the point p is said to lie on the line B. The line is said to pass through p. Additionally, in an incidence geometry any pair of points is joined by at most one line, i.e., |B i B j |1 for all i,j{1,,b}, ij.

An incidence geometry (p,) is called configuration of type (v r ,b k ) if (1) |B j |=k for j=1,2,,b and (2) [p i ]=r for i=1,2,,v. A configuration (p,) with v=b is called symmetric. Its type is simply denoted by v r which is the same as b k because k=r in this case. A configuration C=(p,) is called decomposable if it can be written as the union of two configurations C 1 , C 2 on distinct point sets: C 1 =(p 1 , 1 ), C 2 =(p 2 , 2 ), and P=P 1 P 2 and = 1 2 . Indecomposable configurations are also called connected. The isomorphisms are structure preserving mappings.

A triangle of a configuration consists of three points, say a, b, and c, such that the three pairs {a,b}, {b,c}, {c,a} are contained in different blocks. A configuration that has no triangles is called a triangle-free configuration. An isomorphism CC d is called an anti-automorphism. A configuration which admits an anti-automorphism is called self-dual. An anti-automorphism of order 2 is called a polarity. A configuration which admits a polarity is called self-polar.

The authors give tables of configurations v 3 for v18 and triangle-free configurations for v21 together with some statistics about some properties of structures like transitivity, self-duality or self-polarity.

MSC:
05B30Other designs, configurations