Suppose $X_1$ and $X_2$ are taken at random from a uniform distribution on the interval $[\theta - 1/2, \theta + 1/2]$, where $\theta$ is unknown $(-\infty < \theta < \infty)$. Let $Z = Y_2 - Y_1$, where $Y_1 = min(X_1, X_2)$ and $Y_2 = max(X_1, X_2)$.
How do I calculate the conditional distribution of $X = 0.5(X_1 + X_2)$ given $Z=z$? Specifically, how do I show that this conditional distribution is uniform on the interval $[\theta - 1/2(1 - z), \theta + 1/2(1 - z)]$?