# Co-basis

A co-basis is also called a dual basis. Often the terminology "dual basis" or "co-basis" of $E^*$ is used to denote a basis $(e_i^*)$ of $E^*$ such that $e_i^*(e_j)=\delta_{ij}$ (the Kronecker delta), where $(e_i)$ is a given basis of $E$. The pair $(e_i),(e_i^*)$ is referred to as a pair of dual bases.