Central binomial coefficient: Difference between revisions
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:''This article is a technical mathematical article in the area of predicate logic. For the ordinary English language meaning see [[Sentence (linguistics)]], for a less technical introductory article see [[Statement (logic)]].'' | |||
In [[mathematical logic]], a '''sentence''' of a [[predicate logic]] is a boolean-valued [[well-formed formula]] with no [[Free variables and bound variables|free variables]]. A sentence can be viewed as expressing a [[Proposition (mathematics)|proposition]], something that may be true or false. The restriction of having no free variables is needed to make sure that sentences can have concrete, fixed [[truth value]]s: As the free variables of a (general) formula can range over several values, the truth value of such a formula may vary. | |||
Sentences without any [[logical connective]]s or [[quantifier]]s in them are known as [[atomic sentence]]s; by analogy to [[atomic formula]]. Sentences are then built up out of atomic sentences by applying connectives and quantifiers. | |||
A set of sentences is called a [[Theory (mathematical logic)|theory]]; thus, individual sentences may be called [[theorem]]s. To properly evaluate the truth (or falsehood) of a sentence, one must make reference to an [[interpretation (logic)|interpretation]] of the theory. For first-order theories, interpretations are commonly called [[structure (mathematical logic)|structures]]. Given a structure or interpretation, a sentence will have a fixed [[truth value]]. A theory is [[satisfiable]] when all of its sentences are true. The study of algorithms to automatically discover interpretations of theories that render all sentences as being true is known as the [[satisfiability modulo theories]] problem. | |||
== Example == | |||
The following example is in [[first-order logic]]. | |||
:<math>\forall y\exists x (x^2=y)</math> | |||
''is'' a sentence. This sentence is true in the positive [[real numbers]], false in the real numbers, and true in the complex numbers. (In plain English, this sentence is interpreted to mean that every member of the structure concerned is the [[Square (algebra)|square]] of a member of that particular structure.) On the other hand, the formula | |||
:<math>\exists x(x^2=y)</math> | |||
is ''not'' a sentence, because of the presence of the free variable ''y''. In the structure of the real numbers, this formula is true if we substitute (arbitrarily) ''y'' = 2, but is false if ''y'' = –2. | |||
==See also== | |||
* [[Ground expression]] | |||
* [[Open sentence]] | |||
* [[Statement (logic)]] | |||
* [[Proposition]] | |||
==References== | |||
* {{cite book | author = Hinman, P. | title = Fundamentals of Mathematical Logic | publisher = A K Peters | year = 2005 | isbn = 1-56881-262-0}} | |||
* {{Citation|last=Rautenberg|first=Wolfgang|authorlink=Wolfgang Rautenberg|doi=10.1007/978-1-4419-1221-3|title=A Concise Introduction to Mathematical Logic|url=http://www.springerlink.com/content/978-1-4419-1220-6/|publisher=[[Springer Science+Business Media]]|location=[[New York City|New York]]|edition=3rd|isbn=978-1-4419-1220-6|year=2010}}. | |||
[[Category:Predicate logic]] | |||
[[Category:Propositions]] | |||
{{logic-stub}} | |||
[[fr:Proposition (logique mathématique)]] |
Revision as of 04:27, 16 October 2013
- This article is a technical mathematical article in the area of predicate logic. For the ordinary English language meaning see Sentence (linguistics), for a less technical introductory article see Statement (logic).
In mathematical logic, a sentence of a predicate logic is a boolean-valued well-formed formula with no free variables. A sentence can be viewed as expressing a proposition, something that may be true or false. The restriction of having no free variables is needed to make sure that sentences can have concrete, fixed truth values: As the free variables of a (general) formula can range over several values, the truth value of such a formula may vary.
Sentences without any logical connectives or quantifiers in them are known as atomic sentences; by analogy to atomic formula. Sentences are then built up out of atomic sentences by applying connectives and quantifiers.
A set of sentences is called a theory; thus, individual sentences may be called theorems. To properly evaluate the truth (or falsehood) of a sentence, one must make reference to an interpretation of the theory. For first-order theories, interpretations are commonly called structures. Given a structure or interpretation, a sentence will have a fixed truth value. A theory is satisfiable when all of its sentences are true. The study of algorithms to automatically discover interpretations of theories that render all sentences as being true is known as the satisfiability modulo theories problem.
Example
The following example is in first-order logic.
is a sentence. This sentence is true in the positive real numbers, false in the real numbers, and true in the complex numbers. (In plain English, this sentence is interpreted to mean that every member of the structure concerned is the square of a member of that particular structure.) On the other hand, the formula
is not a sentence, because of the presence of the free variable y. In the structure of the real numbers, this formula is true if we substitute (arbitrarily) y = 2, but is false if y = –2.
See also
References
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