[R-sig-Epi] Left truncated and right censored data

[Martina Gandini]

I have a question concerning a non parametric estimator for left truncated
and right censored data. I see that the function


survfit(Surv(time1, time2, status) ~ group, data=mydata)

  (where time1= left truncation time
   time2= follow=up time
   status= 0:censored 1:not censored)

do this, but what's the method used? Is it a Lynden-Bell (Woodroofe)
estimator or something else?
Regards
Martina Gandini