Duality Interchanges Deletion and Contraction is a result in [matroid theory](/page/Matroid%20Theory). It formalizes the assertion that let be a finite matroid with ground set , and let . Then the matroids on the ground set satisfy \begin{align } (M\setminus e)^ \cong M^ /e. \end{align } Moreover, \begin{align } (M/e)^ \cong M^ \setminus e. \end{align.