# A small question on notation- $\delta_{ij}$ and $\epsilon_{ijk}$ [duplicate]

I'm just reading through some vector calculus notes and it begins to assume knowledge of the notation $\delta_{ij}$ and $\epsilon_{ijk}$ in reference to tensors, but I am not familiar with this. It uses them as if they are constant and well-defined.

If someone could just explain this I would appreciate it. Thank you.

these are well known usefull shorthands.

• While it's unlikely that wikipedia will go down any time soon, we prefer answers on this site that are self-contained, and only use links as supplement. – Arthur Sep 22 '16 at 21:45