When summing an expression using Einstein notation we start with the leftmost index?
For example in that case of $$a^{i}_jb^j_kc^k_l$$
We start with $k$ or $$\sum_{j=1}^{\#}\sum_{k=1}^{\#}a^{i}_jb^j_kc^k_l=a^{i}_1b^1_1c^1_l+a^{i}_1b^1_2c^2_l+a^{i}_1b^1_3c^3_l...$$?
It doesn't matter which order you sum over $j$ and $k$ in. Either way you get the same terms and addition is commutative.