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In mathematical logic, model theory is the study of the relationship between formal theories (a collection of sentences in a formal language expressing statements about a mathematical structure), and their models (those structures in which the statements of the theory hold). [1]
In model theory, a branch of mathematical logic, the diagram of a structure is a simple but powerful concept for proving useful properties of a theory, for example the amalgamation property and the joint embedding property, among others.
Robinson proved that a theory has at most one model companion. Not every theory is model-companionable, e.g. theory of groups. However if T is an -categorical theory, then it always has a model companion. [1] [2] A model completion for a theory T is a model companion T* such that for any model M of T, the theory of T* together with the diagram ...
An interpretation of a structure M in a structure N with parameters (or without parameters, respectively) is a pair (,) where n is a natural number and is a surjective map from a subset of N n onto M such that the -preimage (more precisely the -preimage) of every set X ⊆ M k definable in M by a first-order formula without parameters is definable (in N) by a first-order formula with ...
In model theory and related areas of mathematics, a type is an object that describes how a (real or possible) element or finite collection of elements in a mathematical structure might behave. More precisely, it is a set of first-order formulas in a language L with free variables x 1 , x 2 ,..., x n that are true of a set of n -tuples of an L ...
Model theory is the study of the relationship between formal theories (a collection of sentences in a formal language expressing statements about a mathematical structure), and their models (those structures in which the statements of the theory hold). The aspects investigated include the number and size of models of a theory, the relationship ...
If T is a countable complete theory, then the number I(T, ℵ α) of isomorphism classes of models is given for ordinals α>0 by the minimum of 2 ℵ α and one of the following maps: 2 ℵ α. Examples: there are many examples, in particular any unclassifiable or deep theory, such as the theory of the Rado graph.
In the nomenclature of Vapnik–Chervonenkis theory, we may say that a collection S of subsets of X shatters a set B ⊆ X if every subset of B is of the form B ∩ S for some S ∈ S. Then T has the independence property if in some model M of T there is a definable family (S a | a∈M n) ⊆ M k that shatters arbitrarily large finite subsets ...