[1] " In mathematics, the Kronecker delta (named after Leopold Kronecker) is a function of two variables, usually just positive integers. The function is 1 if the variables are equal, and 0 otherwise:
δ i j = { 0 if i ≠ j , 1 if i = j . {\displaystyle \delta _{ij}={\begin{cases}0&{\text{if...