Etherington's reciprocity theorem (source code)

= Etherington's reciprocity theorem
{wiki=Etherington's_reciprocity_theorem}

Etherington's reciprocity theorem is a result in the field of algebraic geometry and combinatorial mathematics, particularly concerning the enumeration of certain types of geometric configurations known as "dual graphs." The theorem provides a relationship between two different ways of counting the same geometric configuration, particularly relating to how certain properties transform under duality.