library(urca)
data(Raotbl3)
(attach(Raotbl3))
lc <- ts(lc, start=c(1966,4), end=c(1991,2), frequency=4)

lc.ct <- ur.df(lc, lags=3, type='trend')
summary(lc.ct)

lc.co <- ur.df(lc, lags=3, type='drift')
summary(lc.co)

lc.no <- ur.df(lc, lags=3, type='none')
summary(lc.no)

lc2 <- diff(lc)
lc2.ct <- ur.df(lc2, type='trend', lags=3)
summary(lc2.ct)