Internal Set Theory - Formal Axioms For IST

Formal Axioms For IST

IST is an axiomatic theory in the first-order logic with equality in a language containing a binary predicate symbol ∈ and a unary predicate symbol standard(x). Formulas not involving st (i.e., formulas of the usual language of set theory) are called internal, other formulas are called external. We use the abbreviations

\begin{align}\exists^\mathrm{st}x\,\phi(x)&=\exists x\,(\operatorname{standard}(x)\land\phi(x)),\\
\forall^\mathrm{st}x\,\phi(x)&=\forall x\,(\operatorname{standard}(x)\to\phi(x)).\end{align}

IST includes all axioms of the Zermelo–Fraenkel set theory with the axiom of choice (ZFC). Note that the ZFC schemata of separation and replacement are not extended to the new language, they can only be used with internal formulas. Moreover, IST includes three new axiom schemata – conveniently one for each letter in its name: Idealisation, Standardisation, and Transfer.

Read more about this topic:  Internal Set Theory

Famous quotes containing the words formal, axioms and/or ist:

    This is no argument against teaching manners to the young. On the contrary, it is a fine old tradition that ought to be resurrected from its current mothballs and put to work...In fact, children are much more comfortable when they know the guide rules for handling the social amenities. It’s no more fun for a child to be introduced to a strange adult and have no idea what to say or do than it is for a grownup to go to a formal dinner and have no idea what fork to use.
    Leontine Young (20th century)

    The axioms of physics translate the laws of ethics. Thus, “the whole is greater than its part;” “reaction is equal to action;” “the smallest weight may be made to lift the greatest, the difference of weight being compensated by time;” and many the like propositions, which have an ethical as well as physical sense. These propositions have a much more extensive and universal sense when applied to human life, than when confined to technical use.
    Ralph Waldo Emerson (1803–1882)

    God is subtle, but he is not malicious.
    [Raffiniert ist der Herr Gott, aber boshaft ist er nicht.]
    Albert Einstein (1879–1955)