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FinSet
In the mathematical field of category theory, FinSet is the category whose objects are all finite sets and whose morphisms are all functions between them. FinOrd is the category whose objects are all finite ordinal numbers and whose morphisms are all functions between them. Properties FinSet is a full subcategory of Set, the category whose objects are all sets and whose morphisms are all functions. Like Set, FinSet is a large category. FinOrd is a full subcategory of FinSet as by the standard definition, suggested by John von Neumann, each ordinal is the well-ordered set of all smaller ordinals. Unlike Set and FinSet, FinOrd is a small category. FinOrd is a skeleton of FinSet. Therefore, FinSet and FinOrd are equivalent categories. Topoi Like Set, FinSet and FinOrd are topoi. As in Set, in FinSet the categorical product of two objects ''A'' and ''B'' is given by the cartesian product , the categorical sum is given by the disjoint union , and the exponential object ''B''''A' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PRO (category Theory)
In category theory, a branch of mathematics, a PROP is a symmetric strict monoidal category whose objects are the natural numbers ''n'' identified with the finite sets \ and whose tensor product is given on objects by the addition on numbers. Because of “symmetric”, for each ''n'', the symmetric group on ''n'' letters is given as a subgroup of the automorphism group of ''n''. The name PROP is an abbreviation of "PROduct and Permutation category". The notion was introduced by Adams and MacLane; the topological version of it was later given by Boardman and Vogt. Following them, J. P. May then introduced the notion of “operad”, a particular kind of PROP. There are the following inclusions of full subcategories: pg 45 :\mathsf \subset \tfrac\mathsf \subset \mathsf where the first category is the category of (symmetric) operads. Examples and variants An important ''elementary'' class of PROPs are the sets \mathcal^ of ''all'' matrices (regardless of number of rows and colum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Finite Set
In mathematics, particularly set theory, a finite set is a set that has a finite number of elements. Informally, a finite set is a set which one could in principle count and finish counting. For example, :\ is a finite set with five elements. The number of elements of a finite set is a natural number (possibly zero) and is called the '' cardinality (or the cardinal number)'' of the set. A set that is not a finite set is called an ''infinite set''. For example, the set of all positive integers is infinite: :\. Finite sets are particularly important in combinatorics, the mathematical study of counting. Many arguments involving finite sets rely on the pigeonhole principle, which states that there cannot exist an injective function from a larger finite set to a smaller finite set. Definition and terminology Formally, a set is called finite if there exists a bijection :f\colon S\to\ for some natural number . The number is the set's cardinality, denoted as . The empty set o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lawvere Theory
In category theory, a Lawvere theory (named after United States, American mathematician William Lawvere) is a category (mathematics), category that can be considered a categorical counterpart of the notion of an equational theory. Definition Let \aleph_0 be a skeleton (category_theory), skeleton of the category FinSet of finite sets and function (mathematics), functions. Formally, a Lawvere theory consists of a small category ''L'' with (strictly associativity, associative) finite product (category theory), products and a strict identity-on-objects functor (category theory), functor I:\aleph_0^\text\rightarrow L preserving finite products. A model of a Lawvere theory in a category ''C'' with finite products is a finite-product preserving functor . A morphism of models where ''M'' and ''N'' are models of ''L'' is a natural transformation of functors. Category of Lawvere theories A map between Lawvere theories (''L'', ''I'') and (''L''′, ''I''′) is a finite-produc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Skeleton (category Theory)
In mathematics, a skeleton of a category is a subcategory that, roughly speaking, does not contain any extraneous isomorphisms. In a certain sense, the skeleton of a category is the "smallest" equivalent category, which captures all "categorical properties" of the original. In fact, two categories are equivalent if and only if they have isomorphic skeletons. A category is called skeletal if isomorphic objects are necessarily identical. Definition A skeleton of a category ''C'' is an equivalent category ''D'' in which no two distinct objects are isomorphic. It is generally considered to be a subcategory. In detail, a skeleton of ''C'' is a category ''D'' such that: * ''D'' is a subcategory of ''C'': every object of ''D'' is an object of ''C'' :\mathrm(D)\subseteq \mathrm(C) for every pair of objects ''d''1 and ''d''2 of ''D'', the morphisms in ''D'' are morphisms in ''C'', i.e. :\mathrm_D(d_1, d_2) \subseteq \mathrm_C(d_1, d_2) and the identities and compositions in ''D'' a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |