Leigh.Samphier/Sandbox/Definition:Circuit Axioms (Matroid)/Definition 3

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Definition

Let $S$ be a finite set.

Let $\mathscr C$ be a non-empty set of subsets of $S$.


$\mathscr C$ is said to satisfy the circuit axioms if and only if:

\((C1)\)   $:$   \(\ds \O \notin \mathscr C \)             
\((C2)\)   $:$     \(\ds \forall C_1, C_2 \in \mathscr C:\) \(\ds C_1 \ne C_2 \implies C_1 \nsubseteq C_2 \)             
\((C3'')\)   $:$     \(\ds \forall X \subseteq S \land \forall x \in S:\) \(\ds \paren {\forall C \in \mathscr C : C \nsubseteq X} \implies \paren {\exists \text{ at most one } C \in \mathscr C : C \subseteq X \cup \set x} \)             


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