Category:Definitions/Orderings

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This category contains definitions related to Orderings.
Related results can be found in Category:Orderings.


Let $S$ be a set.

Definition 1

$\RR$ is an ordering on $S$ if and only if $\RR$ satisfies the ordering axioms:

\((1)\)   $:$   $\RR$ is reflexive      \(\ds \forall a \in S:\) \(\ds a \mathrel \RR a \)      
\((2)\)   $:$   $\RR$ is transitive      \(\ds \forall a, b, c \in S:\) \(\ds a \mathrel \RR b \land b \mathrel \RR c \implies a \mathrel \RR c \)      
\((3)\)   $:$   $\RR$ is antisymmetric      \(\ds \forall a, b \in S:\) \(\ds a \mathrel \RR b \land b \mathrel \RR a \implies a = b \)      


Definition 2

$\RR$ is an ordering on $S$ if and only if $\RR$ satisfies the ordering axioms:

\((1)\)   $:$   \(\ds \RR \circ \RR \)      
\((2)\)   $:$   \(\ds \RR \cap \RR^{-1} = \Delta_S \)      

where:

$\circ$ denotes relation composition
$\RR^{-1}$ denotes the inverse of $\RR$
$\Delta_S$ denotes the diagonal relation on $S$.