Let $M$ be a matroid on a finite ground set $E$ with rank function $r_M: 2^E \to \mathbb{N} \cup \{0\}$, and let $e \in E$. Let $M \setminus e$ denote the deletion of $e$ and let $M / e$ denote the contraction of $e$, both on the ground set $E \setminus \{e\}$. Then for every subset $A \subset E \setminus \{e\}$,