|
Epsilon-induction
In set theory, \in-induction, also called epsilon-induction or set-induction, is a principle that can be used to prove that all sets satisfy a given property. Considered as an axiomatic principle, it is called the axiom schema of set induction. The principle implies transfinite induction and recursion. It may also be studied in a general context of induction on well-founded relations. Statement The schema is for any given property \psi of sets and states that, if for every set x, the truth of \psi(x) follows from the truth of \psi for all elements of x, then this property \psi holds for all sets. In symbols: :\forall x. \Big(\big(\forall (y \in x). \psi(y)\big)\,\to\,\psi(x)\Big)\,\to\,\forall z. \psi(z) Note that for the "bottom case" where x denotes the empty set \, the subexpression \forall(y\in x).\psi(y) is vacuously true for all propositions and so that implication is proven by just proving \psi(\). In words, if a property is persistent when collecting any sets with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Axiom Of Regularity
In mathematics, the axiom of regularity (also known as the axiom of foundation) is an axiom of Zermelo–Fraenkel set theory that states that every Empty set, non-empty Set (mathematics), set ''A'' contains an element that is Disjoint sets, disjoint from ''A''. In first-order logic, the axiom reads: \forall x\,(x \neq \varnothing \rightarrow (\exists y \in x) (y \cap x = \varnothing)). The axiom of regularity together with the axiom of pairing implies that Russell paradox, no set is an element of itself, and that there is no infinite sequence (a_n) such that a_ is an element of a_i for all i. With the axiom of dependent choice (which is a weakened form of the axiom of choice), this result can be reversed: if there are no such infinite sequences, then the axiom of regularity is true. Hence, in this context the axiom of regularity is equivalent to the sentence that there are no downward infinite membership chains. The axiom was originally formulated by von Neumann; it was adopted in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Axiomatic Set Theory
Set theory is the branch of mathematical logic that studies Set (mathematics), sets, which can be informally described as collections of objects. Although objects of any kind can be collected into a set, set theory – as a branch of mathematics – is mostly concerned with those that are relevant to mathematics as a whole. The modern study of set theory was initiated by the German mathematicians Richard Dedekind and Georg Cantor in the 1870s. In particular, Georg Cantor is commonly considered the founder of set theory. The non-formalized systems investigated during this early stage go under the name of ''naive set theory''. After the discovery of Paradoxes of set theory, paradoxes within naive set theory (such as Russell's paradox, Cantor's paradox and the Burali-Forti paradox), various axiomatic systems were proposed in the early twentieth century, of which Zermelo–Fraenkel set theory (with or without the axiom of choice) is still the best-known and most studied. Set the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Total Relation
In mathematics, a binary relation ''R'' ⊆ ''X''×''Y'' between two sets ''X'' and ''Y'' is total (or left total) if the source set ''X'' equals the domain . Conversely, ''R'' is called right total if ''Y'' equals the range . When ''f'': ''X'' → ''Y'' is a function, the domain of ''f'' is all of ''X'', hence ''f'' is a total relation. On the other hand, if ''f'' is a partial function, then the domain may be a proper subset of ''X'', in which case ''f'' is not a total relation. "A binary relation is said to be total with respect to a universe of discourse just in case everything in that universe of discourse stands in that relation to something else." from |
Law Of Excluded Middle
In logic, the law of excluded middle or the principle of excluded middle states that for every proposition, either this proposition or its negation is true. It is one of the three laws of thought, along with the law of noncontradiction and the law of identity; however, no system of logic is built on just these laws, and none of these laws provides inference rules, such as modus ponens or De Morgan's laws. The law is also known as the law/principle of the excluded third, in Latin ''principium tertii exclusi''. Another Latin designation for this law is ''tertium non datur'' or "no third ossibilityis given". In classical logic, the law is a tautology. In contemporary logic the principle is distinguished from the semantical principle of bivalence, which states that every proposition is either true or false. The principle of bivalence always implies the law of excluded middle, while the converse is not always true. A commonly cited counterexample uses statements unprovable n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of First-order Theories
In first-order logic, a first-order theory is given by a set of axioms in some language. This entry lists some of the more common examples used in model theory and some of their properties. Preliminaries For every natural mathematical structure there is a signature σ listing the constants, functions, and relations of the theory together with their arities, so that the object is naturally a σ-structure. Given a signature σ there is a unique first-order language ''L''σ that can be used to capture the first-order expressible facts about the σ-structure. There are two common ways to specify theories: #List or describe a set of sentences in the language ''L''σ, called the axioms of the theory. #Give a set of σ-structures, and define a theory to be the set of sentences in ''L''σ holding in all these models. For example, the "theory of finite fields" consists of all sentences in the language of fields that are true in all finite ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disjunctive Syllogism
In classical logic, disjunctive syllogism (historically known as ''modus tollendo ponens'' (MTP), Latin for "mode that affirms by denying") is a valid argument form which is a syllogism having a disjunctive statement for one of its premises. An example in English: # I will choose soup or I will choose salad. # I will not choose soup. # Therefore, I will choose salad. Propositional logic In propositional logic, disjunctive syllogism (also known as disjunction elimination and or elimination, or abbreviated ∨E), is a valid rule of inference. If it is known that at least one of two statements is true, and that it is not the former that is true; we can infer that it has to be the latter that is true. Equivalently, if ''P'' is true or ''Q'' is true and ''P'' is false, then ''Q'' is true. The name "disjunctive syllogism" derives from its being a syllogism, a three-step argument, and the use of a logical disjunction (any "or" statement.) For example, "P or Q" is a disjunction, wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Axiom Of Pairing
In axiomatic set theory and the branches of logic, mathematics, and computer science that use it, the axiom of pairing is one of the axioms of Zermelo–Fraenkel set theory. It was introduced by as a special case of his axiom of elementary sets. Formal statement In the formal language of the Zermelo–Fraenkel axioms, the axiom reads: :\forall A \, \forall B \, \exists C \, \forall D \, \in C \iff (D = A \lor D = B)/math> In words: :Given any object ''A'' and any object ''B'', there is a set ''C'' such that, given any object ''D'', ''D'' is a member of ''C'' if and only if ''D'' is equal to ''A'' or ''D'' is equal to ''B''. Consequences As noted, what the axiom is saying is that, given two objects ''A'' and ''B'', we can find a set ''C'' whose members are exactly ''A'' and ''B''. We can use the axiom of extensionality to show that this set ''C'' is unique. We call the set ''C'' the ''pair'' of ''A'' and ''B'', and denote it . Thus the essence of the axiom is: :Any tw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inhabited Set
In mathematics, a set A is inhabited if there exists an element a \in A. In classical mathematics, the property of being inhabited is equivalent to being non- empty. However, this equivalence is not valid in constructive or intuitionistic logic, and so this separate terminology is mostly used in the set theory of constructive mathematics. Definition In the formal language of first-order logic, set A has the property of being if :\exists z. (z \in A). Related definitions A set A has the property of being if \forall z. (z \notin A), or equivalently \neg\exists z. (z \in A). Here z \notin A stands for the negation \neg (z \in A). A set A is if it is not empty, that is, if \neg\forall z. (z \notin A), or equivalently \neg\neg\exists z. (z \in A). Theorems Modus ponens implies P\to((P\to Q)\to Q), and taking any a false proposition for Q establishes that P\to\neg\neg P is always valid. Hence, any inhabited set is provably also non-empty. Discussion In constructive mathematic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Axiom Of Dependent Choice
In mathematics Mathematics is a field of study that discovers and organizes methods, Mathematical theory, theories and theorems that are developed and Mathematical proof, proved for the needs of empirical sciences and mathematics itself. There are many ar ..., the axiom of dependent choice, denoted by \mathsf , is a weak form of the axiom of choice ( \mathsf ) that is still sufficient to develop much of real analysis. It was introduced by Paul Bernays in a 1942 article in reverse mathematics that explores which set-theoretic axioms are needed to develop analysis."The foundation of analysis does not require the full generality of set theory but can be accomplished within a more restricted frame." The axiom of dependent choice is stated on p. 86. Formal statement A homogeneous relation R on X is called a total relation if for every a \in X, there exists some b \in X such that a\,R~b is true. The axiom of dependent choice can be stated as follows: For every ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Axiom Of Replacement
In set theory, the axiom schema of replacement is a schema of axioms in Zermelo–Fraenkel set theory (ZF) that asserts that the image of any set under any definable mapping is also a set. It is necessary for the construction of certain infinite sets in ZF. The axiom schema is motivated by the idea that whether a class is a set depends only on the cardinality of the class, not on the rank of its elements. Thus, if one class is "small enough" to be a set, and there is a surjection from that class to a second class, the axiom states that the second class is also a set. However, because ZFC only speaks of sets, not proper classes, the schema is stated only for definable surjections, which are identified with their defining formulas. Statement Suppose P is a definable binary relation (which may be a proper class) such that for every set x there is a unique set y such that P(x,y) holds. There is a corresponding definable function F_P, where F_P(x)=y if and only if P(x,y). Consid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vacuous Truth
In mathematics and logic, a vacuous truth is a conditional or universal statement (a universal statement that can be converted to a conditional statement) that is true because the antecedent cannot be satisfied. It is sometimes said that a statement is vacuously true because it does not really say anything. For example, the statement "all cell phones in the room are turned off" will be true when no cell phones are present in the room. In this case, the statement "all cell phones in the room are turned ''on''" would also be vacuously true, as would the conjunction of the two: "all cell phones in the room are turned on ''and'' turned off", which would otherwise be incoherent and false. More formally, a relatively well-defined usage refers to a conditional statement (or a universal conditional statement) with a false antecedent. One example of such a statement is "if Tokyo is in Spain, then the Eiffel Tower is in Bolivia". Such statements are considered vacuous truths becau ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antecedent (logic)
An antecedent is the first half of a hypothetical proposition, whenever the if-clause precedes the then-clause. In some contexts the antecedent is called the ''protasis''. Examples: * If P, then Q. This is a nonlogical formulation of a hypothetical proposition. In this case, the antecedent is P, and the consequent is Q. In the implication "\phi implies \psi", \phi is called the antecedent and \psi is called the consequent.Sets, Functions and Logic - An Introduction to Abstract Mathematics, Keith Devlin, Chapman & Hall/CRC Mathematics, 3rd ed., 2004 Antecedent and consequent are connected via logical connective to form a proposition. * If X is a man, then X is mortal. "X is a man" is the antecedent for this proposition while "X is mortal" is the consequent of the proposition. * If men have walked on the Moon, then I am the king of France. Here, "men have walked on the Moon" is the antecedent and "I am the king of France" is the consequent. Let y=x+1. * If x=1 then y=2,. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
