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## Main Question or Discussion Point

Hello!

On page 51 where he want to invert

$$\Lambda^{\mu}_{\nu} = \tfrac{1}{2} \text{tr}( \bar{\sigma}^{\mu}A \sigma_{\nu} A^{\dagger})$$

the person says we may use

$$\sigma_{\nu} A^{\dagger} \bar{\sigma}^{\nu} = 2 \text{tr}(A^{\dagger})I.$$

to do that ... how do you prove this formula?

I have one method which is not good at all, and he does not even prove it so it may be very simple and so I hope you can see it and explain

On page 51 where he want to invert

$$\Lambda^{\mu}_{\nu} = \tfrac{1}{2} \text{tr}( \bar{\sigma}^{\mu}A \sigma_{\nu} A^{\dagger})$$

the person says we may use

$$\sigma_{\nu} A^{\dagger} \bar{\sigma}^{\nu} = 2 \text{tr}(A^{\dagger})I.$$

to do that ... how do you prove this formula?

I have one method which is not good at all, and he does not even prove it so it may be very simple and so I hope you can see it and explain