Let X be a single sample from the double exponential distribution DE(µ, θ) with µ = 0 and θ > 0. Find the UMVUE's of the following parameters and, in each case, determine whether the variance of the UMVUE attains the Cram´er-Rao lower bound.
(a) ϑ = θ;
(b) ϑ = θr, where r > 1;
(c) ϑ = (1 + θ)-1.