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I have a stupid question. It's about the notation used sometimes in the Covariant Derivative.

For example, if somebody tells me:

"If you have a Killing Vector Field [itex]\xi[/itex] with timelike orbits, you can define a time coordinate satisfying [itex]\nabla_{\xi}t=1[/itex]"

what does this last equation means?

I suppose that it has something to be with the normalisation (using +--- signature) , but how do i get the usual [itex]\xi_{a}\xi^{a}=1[/itex] notation from it?$

Thanks in advance!

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# Problem with notation

Can you offer guidance or do you also need help?

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