library(urca)
data(Raotbl3)
attach(Raotbl3)
lc.mod1 <- ur.df(lc, lags=3, type="none")
lc.mod2 <- ur.df(lc, lags=3, type="drift")
lc.mod3 <- ur.df(lc, lags=3, type="trend")
detach(Raotbl3)