Regarding Einstein Summation Convention

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So, I realize the basic theory behind Einstein Summation Convention is that any repeated set of indices implicitly indicates a sum over those indices. However, what if an index is repeated three times?

For example, my mathematics professor posted this problem:

εijkajaj = ?

As you can see, j is repeated thrice. So how do I approach this?
 

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  • #2
dextercioby
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It's nothing to approach, it's incorrect. In a monomial (product of indexed objects) an index can appear no more than 2 times.
 
  • #3
mathman
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So, I realize the basic theory behind Einstein Summation Convention is that any repeated set of indices implicitly indicates a sum over those indices. However, what if an index is repeated three times?

For example, my mathematics professor posted this problem:

εijkajaj = ?

As you can see, j is repeated thrice. So how do I approach this?
It looks like a simple error. ajaj should be aiaj
 

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