DES - Definition of 'Irreducible Subset'

Irreducible Subset:

A closed subset $S\subseteq \mathcal{X}$ is irreducible if every state $j\in S$ is reachable from any other state $i\in S,i\ne j$

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~Example: Irreducible Subset

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~Example: Reducible Subset

State $3$ is not reachable from no other state, so the subset is reducible.