I'm starting to doubt about something:(adsbygoogle = window.adsbygoogle || []).push({});

In 4 dimension, what value has δ[itex]^{λ}_{μ}[/itex] in following equation:

η_{μ[itex]\nu[/itex]}η^{[itex]\nu[/itex]λ}= δ[itex]^{λ}_{μ}[/itex]

is it 4 or 1?

and IF it's 1, what is the difference that this equation:

η^{μσ}η_{μσ}

= 4?

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# Contraction of metrices

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