Please refer to the picture below. In the first line, I define the angular momentum vector $\vec{L} = \vec{R} \times \vec{P}$ using the Levi-Civita tensor $\epsilon^{i}_{jk}$. The definition relies on repeated indices $j$ and $k$.
In the third line, I try to define the scalar $\vec{L}.\vec{L}$ which throws an error possibly because the resulting expression has 4 '$j$' and 4 '$k$' indices (which is nonsensical).
Next, I try to circumvent this problem by using 'ReplaceDummies' which seems to have solved the problem.
Is there another shorter and more elegant way to go because I may not want to stick 'ReplaceDummies' all the time?