diff --git a/cseq/src/elias_fano.rs b/cseq/src/elias_fano.rs
index b9ed2c6..65c6717 100644
--- a/cseq/src/elias_fano.rs
+++ b/cseq/src/elias_fano.rs
@@ -34,10 +34,11 @@ impl<BV> Builder<BV> {
 }
 
 impl<BV: BitVec> Builder<BV> {
-    /// Constructs [`Builder`] to build [`Sequence`] with `final_len` values in range [`0`, `universe`).
+    /// Constructs [`Builder`] to build [`Sequence`] with custom bit vector type and
+    /// `final_len` values in range [`0`, `universe`).
     /// After adding values in non-decreasing order by [`Self::push`] method,
     /// [`Self::finish`] can be called to construct [`Sequence`].
-    pub fn new(final_len: usize, universe: u64) -> Self {
+    pub fn new_b(final_len: usize, universe: u64) -> Self {
         if final_len == 0 || universe == 0 {
             return Self { hi: BV::with_64bit_segments(0, 0), lo: Default::default(), bits_per_lo: 0, current_len: 0, target_len: 0, last_added: 0, universe };
         }
@@ -55,6 +56,15 @@ impl<BV: BitVec> Builder<BV> {
     }
 }
 
+impl Builder {
+    /// Constructs [`Builder`] to build [`Sequence`] with `final_len` values in range [`0`, `universe`).
+    /// After adding values in non-decreasing order by [`Self::push`] method,
+    /// [`Self::finish`] can be called to construct [`Sequence`].
+    #[inline] pub fn new(final_len: usize, universe: u64) -> Self {
+        Self::new_b(final_len, universe)
+    }
+}
+
 impl<BV: DerefMut<Target = [u64]>> Builder<BV> {
     /// A version of [`Self::push`] without any checks and panic.
     pub unsafe fn push_unchecked(&mut self, value: u64) {
@@ -165,6 +175,8 @@ impl<S, S0, BV> Sequence<S, S0, BV> {
 
     /// Returns whether the sequence is empty.
     #[inline] pub fn is_empty(&self) -> bool { self.len == 0 }
+
+    #[inline] pub fn bits_per_lo(&self) -> u8 { self.bits_per_lo }
 }
 
 impl<S, S0, BV: Deref<Target = [u64]>> Sequence<S, S0, BV> {
@@ -307,7 +319,7 @@ impl<S: SelectForRank101111, S0: Select0ForRank101111, BV: BitVec+DerefMut<Targe
     /// Constructs [`Sequence`] with custom select strategy and
     /// filled with elements from the `items` slice, which must be in non-decreasing order.
     pub fn with_items_from_slice_s<I: Into<u64> + Clone>(items: &[I]) -> Self {
-        let mut b = Builder::<BV>::new(items.len(), items.last().map_or(0, |v| v.clone().into()+1));
+        let mut b = Builder::<BV>::new_b(items.len(), items.last().map_or(0, |v| v.clone().into()+1));
         b.push_all(items.iter().map(|v| v.clone().into()));
         b.finish_unchecked_s()
     }
@@ -426,13 +438,22 @@ impl<S, S0: Select0ForRank101111, BV: Deref<Target = [u64]>> Sequence<S, S0, BV>
     }
 }
 
-impl<S: SelectForRank101111, S0> Select for Sequence<S, S0> {
-    #[inline(always)] fn try_select(&self, rank: usize) -> Option<usize> {
+impl<S: SelectForRank101111, S0, BV: Deref<Target = [u64]>> Select for Sequence<S, S0, BV> {
+    #[inline] unsafe fn select_unchecked(&self, rank: usize) -> usize {
+        self.get_unchecked(rank) as usize
+    }
+
+    #[inline] fn try_select(&self, rank: usize) -> Option<usize> {
         self.get(rank).map(|v| v as usize)
     }
 }
 
-impl<S, S0: Select0ForRank101111> Rank for Sequence<S, S0> {
+impl<S, S0: Select0ForRank101111, BV: Deref<Target = [u64]>> Rank for Sequence<S, S0, BV> {
+    /// Returns the number of `self` items with values less than given `value`.
+    #[inline] unsafe fn rank_unchecked(&self, value: usize) -> usize {
+        self.geq_index(value as u64)
+    }
+    
     /// Returns the number of `self` items with values less than given `value`.
     #[inline] fn try_rank(&self, value: usize) -> Option<usize> {
         Some(self.geq_index(value as u64))
diff --git a/cseq_benchmark/src/bitm.rs b/cseq_benchmark/src/bitm.rs
index 66a3fdb..8d96804 100644
--- a/cseq_benchmark/src/bitm.rs
+++ b/cseq_benchmark/src/bitm.rs
@@ -6,7 +6,7 @@ use crate::{percent_of, percent_of_diff, Conf, Tester};
 pub fn build_bit_vec(conf: &Conf) -> (ABox<[u64]>, Tester) {
     let mut content =  ABox::with_zeroed_bits(conf.universe);
     //let mut content = AVec::from_iter(64, (0..ceiling_div(conf.universe, 64)).map(|_| 0)).into_boxed_slice();
-    let tester = conf.rand_data(|bit_nr, value| if value {content.init_bit(bit_nr, value)});
+    let tester = conf.fill_data(|bit_nr, value| if value {content.init_bit(bit_nr, value)});
     (content, tester)
 }
 
diff --git a/cseq_benchmark/src/elias_fano.rs b/cseq_benchmark/src/elias_fano.rs
index 09a12bc..03d2b78 100644
--- a/cseq_benchmark/src/elias_fano.rs
+++ b/cseq_benchmark/src/elias_fano.rs
@@ -1,19 +1,27 @@
 use cseq::elias_fano;
 use dyn_size_of::GetSize;
-use std::{hint::black_box, time::Instant};
 use aligned_vec::ABox;
-use elias_fano::{Sequence, DefaultSelectStrategy as S};
+use elias_fano::Builder;
+use bitm::{Rank, Select};
 
 pub fn benchmark(conf: &super::Conf) {
-    let data: Vec<u64> = (1..=conf.num).map(|i| (i*conf.universe/conf.num) as u64).collect();
-    println!("data contains {} items in the range [0, {})", data.len(), data.last().unwrap()+1);
+    println!("cseq Elias-Fano");
 
-    let start_moment = Instant::now();
-    let ef = Sequence::<S, S, ABox<[u64], _>>::with_items_from_slice_s(&data);
-    let build_time_seconds = start_moment.elapsed().as_secs_f64();
-    println!("size [bits/item]: {:.2}, construction time [μs]: {:.0}", 8.0*ef.size_bytes_dyn() as f64/data.len() as f64, build_time_seconds*1_000_000.0);
+    let mut builder = Builder::<ABox<[u64], _>>::new_b(conf.num(), conf.universe as u64);
+    let tester = conf.add_data(|v| builder.push(v as u64));
 
-    let start_moment = Instant::now();
+    //let start_moment = Instant::now();
+    //let ef = Sequence::<S, S, ABox<[u64], _>>::with_items_from_slice_s(&data);
+    //let build_time_seconds = start_moment.elapsed().as_secs_f64();
+    let ef = builder.finish();
+    println!("  size: {:.2} bits/item   {} bits/lo entry", 8.0*ef.size_bytes() as f64/tester.number_of_ones as f64, ef.bits_per_lo());
+
+    let space_overhead = 100.0 * (8.0*ef.size_bytes() as f64 - conf.universe as f64) / conf.universe as f64;
+
+    tester.raport_rank("cseq Elias-Fano", space_overhead, |i| ef.rank(i));
+    tester.raport_select1("cseq Elias-Fano", space_overhead, |i| ef.select(i));
+
+    /*let start_moment = Instant::now();
     for index in 0..data.len() {
         black_box(ef.get(index));
     }
@@ -34,5 +42,5 @@ pub fn benchmark(conf: &super::Conf) {
             assert_eq!(ef.index_of(v), Some(index), "wrong index for value {v}");
         }
         println!("DONE");
-    }
+    }*/
 }
\ No newline at end of file
diff --git a/cseq_benchmark/src/main.rs b/cseq_benchmark/src/main.rs
index 7385119..0e5df68 100644
--- a/cseq_benchmark/src/main.rs
+++ b/cseq_benchmark/src/main.rs
@@ -278,13 +278,17 @@ impl Conf {
     /// - index in universe in range [0..`self.universe`),
     /// - whether there is an item (one) at the current position.
     /// Print statistics about data. Returns tester.
-    fn rand_data<F: FnMut(usize, bool)>(&self, mut add: F) -> Tester {
+    fn fill_data<F: FnMut(usize, bool)>(&self, mut add: F) -> Tester {
         let number_of_ones = self.data_foreach(|index, _, v| add(index, v));
         println!(" input: number of bit ones is {} / {} ({:.2}%), {} distribution",
             number_of_ones, self.universe, percent_of(number_of_ones, self.universe), self.distribution);
         Tester { conf: self, number_of_ones, rank_includes_current: false }
     }
 
+    #[inline] fn add_data<F: FnMut(usize)>(&self, mut add: F) -> Tester {
+        self.fill_data(|i, v| if v { add(i) })
+    }
+
     /// Either opens or crates (and than put headers inside) and returns the file with given `file_name` (+`csv` extension).
     fn file(&self, file_name: &str, extra_header: &str) -> Option<File> {
         if !self.save_details { return None; }
diff --git a/cseq_benchmark/src/succinct.rs b/cseq_benchmark/src/succinct.rs
index 755f702..5558417 100644
--- a/cseq_benchmark/src/succinct.rs
+++ b/cseq_benchmark/src/succinct.rs
@@ -3,7 +3,7 @@ use crate::{percent_of_diff, Conf, Tester};
 
 pub fn build_bit_vec(conf: &Conf) -> (BitVector::<u64>, Tester) {
     let mut content = BitVector::with_fill(conf.universe as u64, false);
-    let tester = conf.rand_data(|bit_nr, value| {content.set_bit(bit_nr as u64, value)});
+    let tester = conf.fill_data(|bit_nr, value| {content.set_bit(bit_nr as u64, value)});
     (content, tester)
 }
 
diff --git a/cseq_benchmark/src/sucds.rs b/cseq_benchmark/src/sucds.rs
index d01b39d..8fb13c6 100644
--- a/cseq_benchmark/src/sucds.rs
+++ b/cseq_benchmark/src/sucds.rs
@@ -5,7 +5,7 @@ pub fn benchmark_rank9_select(conf: &Conf) {
     println!("sucds Rank9Sel:");
 
     let mut content = BitVector::from_bit(false, conf.universe);
-    let tester = conf.rand_data(|pos, value|
+    let tester = conf.fill_data(|pos, value|
         if value { content.set_bit(pos, value).unwrap(); }
     );
 
diff --git a/cseq_benchmark/src/sux.rs b/cseq_benchmark/src/sux.rs
index 51139f4..c300032 100644
--- a/cseq_benchmark/src/sux.rs
+++ b/cseq_benchmark/src/sux.rs
@@ -4,7 +4,7 @@ use crate::{percent_of_diff, Conf, Tester};
 
 pub fn build_bit_vec(conf: &Conf) -> (BitVec, Tester) {
     let mut content = BitVec::new(conf.universe);
-    let tester = conf.rand_data(|bit_nr, value| content.set(bit_nr, value));
+    let tester = conf.fill_data(|bit_nr, value| content.set(bit_nr, value));
     (content, tester)
 }
 
diff --git a/cseq_benchmark/src/vers.rs b/cseq_benchmark/src/vers.rs
index dd9cb29..918c8ba 100644
--- a/cseq_benchmark/src/vers.rs
+++ b/cseq_benchmark/src/vers.rs
@@ -4,7 +4,7 @@ use crate::percent_of_diff;
 pub fn benchmark_rank_select(conf: &super::Conf) {
     println!("vers:");
     let mut content = BitVec::from_zeros(conf.universe);
-    let tester = conf.rand_data(|pos, value| if value { content.flip_bit(pos); });
+    let tester = conf.fill_data(|pos, value| if value { content.flip_bit(pos); });
 
     let raw_size = content.heap_size();
     let rs = RsVec::from_bit_vec(content);