Equivalence of Definitions of Strict Ordering
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Theorem
Let $S$ be a set.
Let $\RR$ be a relation on $S$.
The following definitions of the concept of Strict Ordering are equivalent:
Definition 1
Let $\RR$ be a relation on a set $S$.
Then $\RR$ is a strict ordering (on $S$) if and only if $\RR$ satisfies the strict ordering axioms:
\((1)\) | $:$ | Asymmetry | \(\ds \forall a, b \in S:\) | \(\ds a \mathrel \RR b \) | \(\ds \implies \) | \(\ds \neg \paren {b \mathrel \RR a} \) | |||
\((2)\) | $:$ | Transitivity | \(\ds \forall a, b, c \in S:\) | \(\ds \paren {a \mathrel \RR b} \land \paren {b \mathrel \RR c} \) | \(\ds \implies \) | \(\ds a \mathrel \RR c \) |
Definition 2
Let $\RR$ be a relation on a set $S$.
Then $\RR$ is a strict ordering (on $S$) if and only if $\RR$ satisfies the strict ordering axioms:
\((1)\) | $:$ | Antireflexivity | \(\ds \forall a \in S:\) | \(\ds \neg \paren {a \mathrel \RR a} \) | |||||
\((2)\) | $:$ | Transitivity | \(\ds \forall a, b, c \in S:\) | \(\ds \paren {a \mathrel \RR b} \land \paren {b \mathrel \RR c} \implies a \mathrel \RR c \) |
Proof
Let $\RR$ be transitive.
Then by Transitive Relation is Antireflexive iff Asymmetric it follows directly that:
- $(1): \quad$ If $\RR$ is antireflexive then it is asymmetric
- $(2): \quad$ If $\RR$ is asymmetric then it is antireflexive.
$\blacksquare$