Synopsis:

• The unit Cartesian tensor (delta[i,j] = 1 if i=j, 0 otherwise). To be used with &t and nab(.)[i] to form general Cartesian tensor expressions.

Examples:

> delta[1,1];
                                       1
> delta[1,2];
                                       0
> A[i,j] &t delta[j,k] &t b[k,n];
              A[i, 1] b[1, n] + A[i, 2] b[2, n] + A[i, 3] b[3, n]