Definition:Transitive Closure (Relation Theory)/Finite Chain

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Let $\mathcal R$ be a relation on a set or class $S$.

The transitive closure of $\mathcal R$ is the relation $\mathcal R^+$ defined as follows:

For $x, y \in S$, $x \mathrel {\mathcal R^+} y$ if and only if for some $n \in \N_{>0}$ there exist $s_0, s_1, \dots, s_n \in S$ such that $s_0 = x$, $s_n = y$, and:

\(\displaystyle s_0\) \(\mathcal R\) \(\displaystyle s_1\)
\(\displaystyle s_1\) \(\mathcal R\) \(\displaystyle s_2\)
\(\displaystyle \) \(\vdots\) \(\displaystyle \)
\(\displaystyle s_{n - 1}\) \(\mathcal R\) \(\displaystyle s_n\)

That is:

$\forall k \in \N_n: s_k \mathrel {\mathcal R} s_{k+1}$