Transitive Class/Examples/Class with Empty Class and its Singleton
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Example of Transitive Class
Let $\O$ denote the empty class.
Then the class:
- $\set {\O, \set \O}$
is transitive.
Proof
Consider the elements of $\set {\O, \set \O}$ in turn.
There are no elements of $\O$.
There is exactly one elements of $\set \O$, and that is $\O$.
We see that $\O$ is itself an element of $\set {\O, \set \O}$.
Thus all elements of elements of $\set {\O, \set \O}$ are themselves elements of $\set {\O, \set \O}$.
Hence by definition $\set {\O, \set \O}$ is transitive.
$\blacksquare$
Sources
- 2010: Raymond M. Smullyan and Melvin Fitting: Set Theory and the Continuum Problem (revised ed.) ... (previous) ... (next): Chapter $2$: Some Basics of Class-Set Theory: $\S 10$ Some useful facts about transitivity