06.1 Duality
6.1 Duality Duality is a recurring pattern in mathematics where one concept is paired with another by reversing roles, directions, or operations. A statement about one object often has a corresponding statement about its dual, obtained by systematically exchanging parts of the structure. At a simple level, duality appears in operations. Intersection and union of sets behave as opposites under complement: $$ (A \cup B)^c = A^c \cap B^c, \quad...