# Kronecker delta

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Please note that this does not mean the content is unreliable, it just means that the author of the page doesn't have a book to hand, or remember the book to find it, which would have been a suitable reference.
The message provided is:
This is VERY common and the name isn't disputed, there's no ambiguity because it doesn't matter what way the arguments go. as such this is a low priority for finding references for
• $\delta_j^i:=\left\{\begin{array}{lr}1 & \text{if }i=j\\0&\text{otherwise}\end{array}\right.$