Demonstrate that for a closed path (operatorname{Tr} U_{gamma}(x, x)) is gauge invariant, where (U_{gamma}left(x_{0}, x_{1} ight)) is

Demonstrate that for a closed path \(\operatorname{Tr} U_{\gamma}(x, x)\) is gauge invariant, where \(U_{\gamma}\left(x_{0}, x_{1}\right)\) is defined by Eq. (26.9).