+/** Return the reduced matrix that is formed by deleting the rth row and cth
+ * column of matrix m. The determinant of the result is the Minor r, c. */
+extern ex reduced_matrix(const matrix& m, unsigned r, unsigned c);
+
+/** Return the nr times nc submatrix starting at position r, c of matrix m. */
+extern ex sub_matrix(const matrix&m, unsigned r, unsigned nr, unsigned c, unsigned nc);
+