Axiom:Axioms of Class Existence

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Axiom

Let the ordered pair notation be understood to denote:

$\tuple {X, Y} := \set {\set X, \set {X, Y}}$

that is, the Kuratowski formalization of ordered pairs.


The following are the axioms of class existence:

\((\text B 1)\)   $:$   \(\ds \exists X: \forall u, v: \tuple {u, v} \in X \iff u \in v \)      $\in$-relation
\((\text B 2)\)   $:$   \(\ds \forall X, Y: \exists Z: \forall u: u \in Z \iff u \in X \land u \in Y \)      intersection
\((\text B 3)\)   $:$   \(\ds \forall X: \exists Z: \forall u: u \in Z \iff u \notin X \)      complement
\((\text B 4)\)   $:$   \(\ds \forall X: \exists Z: \forall u: u \in Z \iff \exists v: \tuple {u, v} \in X \)      domain
\((\text B 5)\)   $:$   \(\ds \forall X: \exists Z: \forall u, v: \tuple {u, v} \in Z \iff u \in X \)      
\((\text B 6)\)   $:$   \(\ds \forall X: \exists Z: \forall u, v, w: \tuple {\tuple {u, v}, w} \in Z \iff \tuple {\tuple {v, w}, u} \in X \)      
\((\text B 7)\)   $:$   \(\ds \forall X: \exists Z: \forall u, v, w: \tuple {\tuple {u, v}, w} \in Z \iff \tuple {\tuple {u, w}, v} \in X \)      


Sources