diff --git a/CHANGELOG.txt b/CHANGELOG.txt
index 44ed2ef..a3ea45c 100644
--- a/CHANGELOG.txt
+++ b/CHANGELOG.txt
@@ -2372,3 +2372,26 @@ Propagated typo corrections into the docs.
 *****
 
 Updated link of license badge to point to RTD docs. 
+
+
+*****  Sat Jun 12 19:01:21 CEST 2021  *****
+
+In bm.remove_dubplicates() added additional check for DOI after
+identical ISBN values in case the entries refer to different chapters
+of a same book.
+Added respective tests.
+
+*****
+
+Small tweak to docs (put latest tutorial video first).
+
+*****
+
+Bumped bibmanager to version 1.3.4
+
+*****
+
+Added mock_init to test_duplicate_isbn_same_unknown_doi() tests
+because the code needs the config file initialized to set the screen
+output style.
+
diff --git a/bibmanager/VERSION.py b/bibmanager/VERSION.py
index 1d5038e..c3c2aca 100644
--- a/bibmanager/VERSION.py
+++ b/bibmanager/VERSION.py
@@ -2,4 +2,4 @@
 # bibmanager is open-source software under the MIT license (see LICENSE).
 
 # bibmanager Version:
-__version__ = "1.3.3"
+__version__ = "1.3.4"
diff --git a/bibmanager/bib_manager/bib_manager.py b/bibmanager/bib_manager/bib_manager.py
index 20aa2fe..a8a00a3 100644
--- a/bibmanager/bib_manager/bib_manager.py
+++ b/bibmanager/bib_manager/bib_manager.py
@@ -461,6 +461,22 @@ def remove_duplicates(bibs, field):
         if nbibs == 1:
             continue
 
+        # If field is isbn, check doi to differentiate chapters from same book:
+        if field == 'isbn':
+            dois = [
+                bibs[idx].doi if bibs[idx].doi is not None else ""
+                for idx in indices]
+            u_doi, doi_inv, doi_counts = np.unique(
+                dois, return_inverse=True, return_counts=True)
+            doi_multis = np.where((doi_counts > 1) & (ubib != ""))[0]
+            single_dois = u_doi[doi_counts==1]
+            indices = [
+                idx for idx,doi in zip(indices,dois)
+                if doi not in single_dois]
+            nbibs = len(indices)
+            if nbibs <= 1:
+                continue
+
         # Query the user:
         labels = [idx + " ENTRY:\n" for idx in u.ordinal(np.arange(nbibs)+1)]
         display_bibs(labels, [bibs[i] for i in indices])
diff --git a/docs/index.rst b/docs/index.rst
index 3a49ea1..63494ca 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -50,13 +50,13 @@ Check out this video tutorial to get started with ``bibmanager``:
 
 .. raw:: html
 
-    <iframe width="720" height="405" src="https://www.youtube.com/embed/WVmhdwVNXOE" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
+    <iframe width="720" height="405" src="https://www.youtube.com/embed/qewdBx0M8VE" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
 
-And the new features for version 1.3+:
+And this one covering some other features:
 
 .. raw:: html
 
-    <iframe width="720" height="405" src="https://www.youtube.com/embed/qewdBx0M8VE" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
+    <iframe width="720" height="405" src="https://www.youtube.com/embed/WVmhdwVNXOE" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
 
 
 .. _team:

diff --git a/tests/conftest.py b/tests/conftest.py
index 501e67a..e6c810b 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -233,20 +233,58 @@ archivePrefix = "arXiv",
   publisher={AIP Publishing}
 }"""
 
+    isbn_doi1 = """
+@INBOOK{2018haex.bookE.116P,
+       author = {{Parmentier}, Vivien and {Crossfield}, Ian J.~M.},
+        title = "{Exoplanet Phase Curves: Observations and Theory}",
+         year = 2018,
+          doi = {10.1007/978-3-319-55333-7\_116},
+         isbn = "978-3-319-55333-7",
+}"""
+
+    isbn_doi2 = """
+@INBOOK{2018haex.bookE.147C,
+       author = {{Cowan}, Nicolas B. and {Fujii}, Yuka},
+        title = "{Mapping Exoplanets}",
+         year = 2018,
+          doi = {10.1007/978-3-319-55333-7\_147},
+         isbn = "978-3-319-55333-7",
+}"""
+
+    isbn_no_doi1 = """
+@INBOOK{2018haex.bookE.116P,
+       author = {{Parmentier}, Vivien and {Crossfield}, Ian J.~M.},
+        title = "{Exoplanet Phase Curves: Observations and Theory}",
+         year = 2018,
+         isbn = "978-3-319-55333-7",
+}"""
+
+    isbn_no_doi2 = """
+@INBOOK{2018haex.bookE.147C,
+       author = {{Cowan}, Nicolas B. and {Fujii}, Yuka},
+        title = "{Mapping Exoplanets}",
+         year = 2018,
+         isbn = "978-3-319-55333-7",
+}"""
+
     data = {
-        'jones_minimal':      jones_minimal,
-        'jones_no_year':      jones_no_year,
-        'jones_no_title':     jones_no_title,
-        'jones_no_author':    jones_no_author,
-        'jones_braces':       jones_braces,
-        'beaulieu_apj':       beaulieu_apj,
-        'beaulieu_arxiv':     beaulieu_arxiv,
+        'jones_minimal': jones_minimal,
+        'jones_no_year': jones_no_year,
+        'jones_no_title': jones_no_title,
+        'jones_no_author': jones_no_author,
+        'jones_braces': jones_braces,
+        'beaulieu_apj': beaulieu_apj,
+        'beaulieu_arxiv': beaulieu_arxiv,
         'beaulieu_arxiv_dup': beaulieu_arxiv_dup,
-        'hunter':             hunter,
-        'oliphant_dup':       oliphant_dup,
-        'no_oliphant':        no_oliphant,
-        'sing':               sing,
-        'stodden':            stodden,
+        'hunter': hunter,
+        'oliphant_dup': oliphant_dup,
+        'no_oliphant': no_oliphant,
+        'sing': sing,
+        'stodden': stodden,
+        'isbn_doi1': isbn_doi1,
+        'isbn_doi2': isbn_doi2,
+        'isbn_no_doi1': isbn_no_doi1,
+        'isbn_no_doi2': isbn_no_doi2,
            }
     return data
 
diff --git a/tests/test_bib_manager.py b/tests/test_bib_manager.py
index 83edf8d..10922b9 100644
--- a/tests/test_bib_manager.py
+++ b/tests/test_bib_manager.py
@@ -801,6 +801,29 @@ def test_merge_duplicate_title_add(bibs, mock_init_sample, mock_input):
     assert bibs['no_oliphant'] in loaded_bibs
 
 
+def test_duplicate_isbn_different_doi(capfd, entries):
+    text = entries['isbn_doi1'] + entries['isbn_doi2']
+    bibs = bm.read_file(text=text)
+    assert len(bibs) == 2
+    captured = capfd.readouterr()
+    assert captured.out == ''
+
+
+def test_duplicate_isbn_doi_vs_no_doi(capfd, entries):
+    text = entries['isbn_doi1'] + entries['isbn_no_doi2']
+    bibs = bm.read_file(text=text)
+    assert len(bibs) == 2
+    captured = capfd.readouterr()
+    assert captured.out == ''
+
+
+@pytest.mark.parametrize('mock_input', [['']], indirect=True)
+def test_duplicate_isbn_same_unknown_doi(mock_init, mock_input, entries):
+    text = entries['isbn_no_doi1'] + entries['isbn_no_doi2']
+    bibs = bm.read_file(text=text)
+    assert len(bibs) == 1
+
+
 def test_init_from_scratch(mock_home):
     shutil.rmtree(u.HOME, ignore_errors=True)
     bm.init(bibfile=None)

ISBN duplicates problem
An edited book has many contributions. Each contribution has its own DOI number, but also shares its parent book's ISBN. Contributions and parent reference are now regarded as duplicates in bibmanager and merge always triggers asking. I have tried to disable exporting ISBN of contributions to bibfile. And this solved the annoyance of asking. But if only focusing on bibfile, this workaround seems lost ISBN information then. Is there a better way to settle this problem down?
tests/test_bib_manager.py::test_duplicate_isbn_different_doi tests/test_bib_manager.py::test_duplicate_isbn_doi_vs_no_doi
tests/test_bib_manager.py::test_Bib_minimal tests/test_bib_manager.py::test_Bib_ads_entry tests/test_bib_manager.py::test_Bib_update_content tests/test_bib_manager.py::test_Bib_mismatched_braces_raise tests/test_bib_manager.py::test_Bib_update_key tests/test_bib_manager.py::test_Bib_contains tests/test_bib_manager.py::test_Bib_published_peer_reviewed tests/test_bib_manager.py::test_Bib_published_arxiv tests/test_bib_manager.py::test_Bib_published_non_ads tests/test_bib_manager.py::test_Bib_month[-13] tests/test_bib_manager.py::test_Bib_month[month tests/test_bib_manager.py::test_Bib_lower_than_no_author tests/test_bib_manager.py::test_Bib_lower_than_both_no_author tests/test_bib_manager.py::test_Bib_lower_than_no_year tests/test_bib_manager.py::test_Bib_equal_no_author tests/test_bib_manager.py::test_Bib_equal_both_no_author tests/test_bib_manager.py::test_Bib_not_equal_both_no_author tests/test_bib_manager.py::test_Bib_not_equal_no_year tests/test_bib_manager.py::test_Bib_equal_no_year tests/test_bib_manager.py::test_Bib_meta tests/test_bib_manager.py::test_Bib_warning_year tests/test_bib_manager.py::test_Bib_warning_month[15] tests/test_bib_manager.py::test_Bib_warning_month[tuesday] tests/test_bib_manager.py::test_Bib_warning_authors_comma_typo tests/test_bib_manager.py::test_Bib_warning_authors_missing_and tests/test_bib_manager.py::test_remove_duplicates_no_duplicates tests/test_bib_manager.py::test_remove_duplicates_identical tests/test_bib_manager.py::test_remove_duplicates_diff_published tests/test_bib_manager.py::test_remove_duplicates_query[mock_input0] tests/test_bib_manager.py::test_filter_field_no_conflict tests/test_bib_manager.py::test_filter_field_take_published tests/test_bib_manager.py::test_filter_field_take_old tests/test_bib_manager.py::test_filter_field_take_new tests/test_bib_manager.py::test_filter_field_take_ask[mock_input0] tests/test_bib_manager.py::test_filter_field_take_ask2[mock_input0] tests/test_bib_manager.py::test_read_file_bibfile tests/test_bib_manager.py::test_read_file_text tests/test_bib_manager.py::test_read_file_single_line_entry tests/test_bib_manager.py::test_read_file_ignore_comment tests/test_bib_manager.py::test_read_file_ignore_comment_no_commas tests/test_bib_manager.py::test_read_file_meta tests/test_bib_manager.py::test_read_file_pdf_with_path tests/test_bib_manager.py::test_read_file_pdf_with_bad_path tests/test_bib_manager.py::test_read_file_error_bad_format tests/test_bib_manager.py::test_read_file_error_open_end tests/test_bib_manager.py::test_save tests/test_bib_manager.py::test_load tests/test_bib_manager.py::test_load_filed tests/test_bib_manager.py::test_find_key tests/test_bib_manager.py::test_find_bibcode tests/test_bib_manager.py::test_find_key_bibcode tests/test_bib_manager.py::test_find_key_not_found tests/test_bib_manager.py::test_find_bibcode_not_found tests/test_bib_manager.py::test_find_bibs tests/test_bib_manager.py::test_find_no_arguments tests/test_bib_manager.py::test_get_version_older tests/test_bib_manager.py::test_get_version_no_pickle tests/test_bib_manager.py::test_get_version_existing tests/test_bib_manager.py::test_get_version_filed tests/test_bib_manager.py::test_export_home tests/test_bib_manager.py::test_export_no_overwrite tests/test_bib_manager.py::test_export_meta tests/test_bib_manager.py::test_export_no_meta tests/test_bib_manager.py::test_merge_bibfile tests/test_bib_manager.py::test_merge_bibs tests/test_bib_manager.py::test_merge_no_new tests/test_bib_manager.py::test_merge_base tests/test_bib_manager.py::test_merge_bibs_no_titles tests/test_bib_manager.py::test_merge_duplicate_key_ingnore[mock_input0] tests/test_bib_manager.py::test_merge_duplicate_key_rename[mock_input0] tests/test_bib_manager.py::test_merge_duplicate_title_ignore[mock_input0] tests/test_bib_manager.py::test_merge_duplicate_title_add[mock_input0] tests/test_bib_manager.py::test_duplicate_isbn_same_unknown_doi[mock_input0] tests/test_bib_manager.py::test_init_from_scratch tests/test_bib_manager.py::test_add_entries_dry[mock_prompt0] tests/test_bib_manager.py::test_add_entries[mock_prompt0] tests/test_bib_manager.py::test_search_author_lastname tests/test_bib_manager.py::test_search_author_last_initials tests/test_bib_manager.py::test_search_author_first tests/test_bib_manager.py::test_search_author_multiple tests/test_bib_manager.py::test_search_author_year_title tests/test_bib_manager.py::test_search_title_multiple tests/test_bib_manager.py::test_search_title_entry_without_title tests/test_bib_manager.py::test_search_year_specific tests/test_bib_manager.py::test_search_year_range tests/test_bib_manager.py::test_search_bibcode tests/test_bib_manager.py::test_search_bibcode_utf8 tests/test_bib_manager.py::test_search_bibcode_multiple tests/test_bib_manager.py::test_search_key tests/test_bib_manager.py::test_search_key_multiple tests/test_bib_manager.py::test_prompt_search_kw1[mock_prompt_session0] tests/test_bib_manager.py::test_prompt_search_kw2[mock_prompt_session0] tests/test_bib_manager.py::test_prompt_search_extra[mock_prompt_session0] tests/test_bib_manager.py::test_prompt_search_empty_prompt[mock_prompt_session0] tests/test_bib_manager.py::test_prompt_search_empty_value[mock_prompt_session0] tests/test_bib_manager.py::test_prompt_search_blank_value[mock_prompt_session0] tests/test_bib_manager.py::test_prompt_search_double_def[mock_prompt_session0]