Identity Minus Compact Linear Operator on Banach Space has Index Zero

Theorem
Let $\struct {X, \norm \cdot_X}$ be a Banach space.

Let $I : X \to X$ be the identity mapping.

Let $C : X \to X$ be a compact linear operator.

Then $I - C$ has finite index with the index:
 * $\map {\mathrm{ind} } {I - C} = 0$