n <- 10000
alpha <- 2
beta <- 3
x <- runif(n)
p <- function(x) dunif(x)
q <- function(x) dbeta(x,alpha,beta)
w <- q(x)/p(x)
pi <- w/sum(w)
samp <- sample(x,size=n,prob=pi,replace=T)
print(mean(samp))
print(var(samp))