Since we are summing over the repeated index i, we have

vⁱ_i^j = v¹(0) + v²(0) + ... + v^j-1(0) + v^j(1) + v^j+1(0) + ... + vⁿ(0)
      = v^j.

In other words, the effect of _i^j in front of an expression is to substitute j for i, as though the i's cancel.

(Similarly, v_ji^j = v_i).

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