suppose I have a multiple sum with an unspecified number of indexes:

$$\sum_{i_1=1}^n \ldots \sum_{i_k=1}^n x_{i_1}\otimes\ldots\otimes \hat{x_{i_j}}\otimes\ldots\otimes x_{i_k}$$

with $x_{i_j}$ being omitted in the sum. The number $n$ is a positive integer. We can simplify this expression to $$n \sum_{i_1=1}^n \ldots \sum_{i_{k-1}=1}^n x_{i_1}\otimes\ldots\otimes x_{i_{k-1}},$$

but my frail attempts at teaching this to Mathematica 6 have tremendously failed. It won't accept any pattern of type

Sum[x_, y___, {k_, l_, m_}, z___] /; FreeQ[x, k] :> (m - l) Sum[x, y, z].

complaining about y___ not being an iterator.

Please help :)

  • 1
    $\begingroup$ Do you know the function HoldPattern? $\endgroup$ – halirutan Apr 14 '15 at 12:17
  • $\begingroup$ Now, I do, thanks :) $\endgroup$ – Mischa Apr 17 '15 at 7:37
  • $\begingroup$ This Link can also be useful. $\endgroup$ – H. R. Mar 27 '17 at 12:07

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