# Leigh.Samphier/Sandbox/Proper Subset of Matroid Circuit is Independent

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## Theorem

Let $M = \struct {S, \mathscr I}$ be a matroid.

Let $C \subseteq S$ be a circuit of $M$.

Then:

- every proper subset $A$ of $C$ is independent

## Proof

By definition of a circuit of $M$:

- $C$ is a minimum dependent subset of $M$

By definition of the minimum dependent subset of $M$:

- every proper subset $A$ of $C$ is not a dependent subset

By definition of a dependent subset:

- every proper subset $A$ of $C$ is an independent subset

$\blacksquare$

## Sources

- 1976: Dominic Welsh:
*Matroid Theory*... (previous) ... (next) Chapter $1.$ $\S 9.$ Circuits