Good evening,

I wish to build an array containing specific multi-index. More precisely, in the 2-D case the multi-index are given by `(i, j)`

where `0 <= i , j <= N+1`

such that `i+j <= N+1`

. The way I do it is make a (N+1)x(N+1) array and cut it in two along its anti-diagonal, namely

```
βtab = CartesianIndices((N+1, N+1))
βtab = Tuple.( vec(rotl90( UpperTriangular( rotr90(βtab) ) )) )
filter!(x -> sum(x) ≠ 0, βtab)
```

Does Julia have features that could be used to implement this in a more elegant way ?