cdp(v)={
  my(s="");
  v=apply(t->Vec(t),v);
  for(i=1,vecmin(apply(length,v)),
    for(j=2,#v,
      if(v[j][i]!=v[1][i],return(s)));
      if(i>1&v[1][i]=="/",s=concat(vecextract(v[1],1<<(i-1)-1))
    )
  );
  if(vecmax(apply(length,v))==vecmin(apply(length,v)),concat(v[1]),s)
};
cdp(["/home/user1/tmp/coverage/test","/home/user1/tmp/covert/operator","/home/user1/tmp/coven/members"])