Axiom:Rank Axioms (Matroid)/Definition 1

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Let $S$ be a finite set.

Let $\rho: \powerset S \to \Z$ be a mapping from the power set of $S$ into the integers.

$\rho$ is said to satisfy the rank axioms if and only if:

\((\text R 1)\)   $:$   \(\ds \map \rho \O = 0 \)      
\((\text R 2)\)   $:$     \(\ds \forall X \in \powerset S \land y \in S:\) \(\ds \map \rho X \le \map \rho {X \cup \set y} \le \map \rho X + 1 \)      
\((\text R 3)\)   $:$     \(\ds \forall X \in \powerset S \land y, z \in S:\) \(\ds \map \rho {X \cup \set y} = \map \rho {X \cup \set z} = \map \rho X \implies \map \rho {X \cup \set y \cup \set z} = \map \rho X \)      

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