Definition:Transitive Relation

Definition

Let $\mathcal R \subseteq S \times S$ be a relation in $S$.

$\mathcal R$ is transitive if and only if:

$\tuple {x, y} \in \mathcal R \land \tuple {y, z} \in \mathcal R \implies \tuple {x, z} \in \mathcal R$

that is:

$\set {\tuple {x, y}, \tuple {y, z} } \subseteq \mathcal R \implies \tuple {x, z} \in \mathcal R$

$\mathcal R$ is transitive if and only if:

$\mathcal R \circ \mathcal R \subseteq \mathcal R$

where $\circ$ denotes composite relation.

Let $P$ be the set of people.

Let $\sim$ be the relation on $P$ defined as:

$\forall \tuple {x, y} \in P \times P: x \sim y \iff \text { $x$ is an ancestor of $y$}$