diff --git a/indexation.cabal b/indexation.cabal
--- a/indexation.cabal
+++ b/indexation.cabal
@@ -1,5 +1,5 @@
 name: indexation
-version: 0.4.8
+version: 0.4.9
 category: Data
 synopsis: Tools for entity indexation
 description: A set of tools for indexing entities
diff --git a/library/Indexation/Functions.hs b/library/Indexation/Functions.hs
--- a/library/Indexation/Functions.hs
+++ b/library/Indexation/Functions.hs
@@ -47,3 +47,9 @@
 
 indexSetByMinCount :: Word32 -> IndexCounts a -> IndexSet a
 indexSetByMinCount min (IndexCounts countVec) = IndexSet (UnboxedVector.map (Bit.fromBool . (>= min)) countVec)
+
+countIndexSet :: IndexSet a -> Int
+countIndexSet (IndexSet vec) = BitVec.countBits vec
+
+invertIndexSet :: IndexSet a -> IndexSet a
+invertIndexSet (IndexSet vec) = IndexSet (BitVec.invert vec)