st: restrict subjects for analysis from multi-record data

["KUBO Tatsuhiko" <kubo@med.uoeh-u.ac.jp>]

Dear colleges,

I am now making a survival analysis using the multi-record data.

Now, I want to restrict the subjects for analysis regarding their life 
styles.
  >>  e.g. make analysis only among subjects who are smokers (smoke==1) at 
the time of the baseline(_t0==0).
  >>  e.g. make analysis only among subjects who are smokers at the time of 
the endpoint.

In this case what command should be used to restrict the subjects?


Thank you.