# How to evaluate an expression with FeynCalc?

How can I evaluate specific expressions in FeynCalc? For example, if there is a $$\delta^i_j$$, how can I set $$i$$ to 1 and $$j$$ to 2 and make it evaluate to zero?

I've tried

TR[GA[µ,v]] /. {µ -> 1, v -> 2}


but that does not work, it just yields $$4g^{12}$$ instead of 0.

Pair[LorentzIndex[1], LorentzIndex[2]] = 0