diff --git a/README.md b/README.md
index f6ec1b4273e59593f49488c637506ca8d19f45f7..ee0e60beedfbb337948728c34f6680a4a25c2608 100644
--- a/README.md
+++ b/README.md
@@ -77,19 +77,21 @@ instead of `bytes(record.seq)`.
 import pyfastani
 import Bio.SeqIO
 
-m = pyfastani.Mapper()
+sketch = pyfastani.Sketch()
 
 # add a single draft genome to the mapper, and index it
 ref = list(Bio.SeqIO.parse("vendor/FastANI/data/Shigella_flexneri_2a_01.fna", "fasta"))
-m.add_draft("Shigella_flexneri_2a_01", (bytes(record.seq) for record in ref))
-m.index()
+sketch.add_draft("S. flexneri", (bytes(record.seq) for record in ref))
+
+# index the sketch and get a mapper
+mapper = sketch.index()
 
 # read the query and query the mapper
 query = Bio.SeqIO.read("vendor/FastANI/data/Escherichia_coli_str_K12_MG1655.fna", "fasta")
 hits = m.query_sequence(bytes(query.seq))
 
 for hit in hits:
-    print("Escherichia_coli_str_K12_MG1655", hit.name, hit.identity, hit.matches, hit.fragments)
+    print("E. coli", hit.name, hit.identity, hit.matches, hit.fragments)
 ```
 
 ### 🧪 [Scikit-bio](https://github.com/biocore/scikit-bio)
diff --git a/pyfastani/_fastani.pyx b/pyfastani/_fastani.pyx
index 27575b1cf6623b17785d3fa211eef041fdfd50fc..94c173ddf0656c7b3fb0c6b50135fef08b0ea108 100644
--- a/pyfastani/_fastani.pyx
+++ b/pyfastani/_fastani.pyx
@@ -363,11 +363,10 @@ cdef class Sketch:
         cdef Mapper mapper = Mapper.__new__(Mapper)
         mapper._param = self._param # copy params
         mapper._sk = self._sk
-        mapper._names = self._names
+        mapper._names = self._names.copy()
         mapper._lengths.swap(self._lengths)
         # reset the current sketch
         self._sk = new Sketch_t(self._param)
-        self._names = []
         self.clear()
         # return the new mapper
         return mapper
@@ -517,13 +516,18 @@ cdef class Mapper:
             contigs (iterable or `str` or `bytes`): The genome to query the mapper
                 with.
 
-        Note:
+        Returns:
+            `list` of `~pyfastani.Hit`: The hits found for the query.
+
+        Hint:
             Sequence must be larger than the window size, the k-mer size,
             and the fragment length to be mapped, otherwise an empty list
             of hits will be returned.
 
-        Returns:
-            `list` of `~pyfastani.Hit`: The hits found for the query.
+        Note:
+            This method is reentrant and releases the GIL when hashing
+            the blocks allowing to query the mapper in parallel for
+            several individual genomes.
 
         """
         # delegate to C code
@@ -538,13 +542,18 @@ cdef class Mapper:
             sequence (`str` or `bytes`): The genome to query the mapper
                 with.
 
-        Note:
+        Returns:
+            `list` of `~pyfastani.Hit`: The hits found for the query.
+
+        Hint:
             Sequence must be larger than the window size, the k-mer size,
             and the fragment length to be mapped, otherwise an empty list
             of hits will be returned.
 
-        Returns:
-            `list` of `~pyfastani.Hit`: The hits found for the query.
+        Note:
+            This method is reentrant and releases the GIL when hashing
+            the blocks allowing to query the mapper in parallel for
+            several individual genomes.
 
         """
         # delegate to C code