Then, ifIf you transform a variable then the mean and the mode may vary due to this change of the distribution function. That means $\bar{x} \neq \chi(\bar{\xi})$ and $x_{\max f(x)} \neq \chi(\xi_{\max f(\xi)})$.
The likelihood function does not transform in this way. This is the contrasts between the likelihood function and the posterior probability. The maximum(maximum of the) likelihood function remains the same when you transform the variable $x_{\max \mathcal{L}(x)} = \chi(\xi_{\max \mathcal{L}(\xi)})$.
As a result$$\mathcal{L}_\xi(\xi) = \mathcal{L}_x(\chi(\xi)) $$
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