diff --git a/libcodonusage/libcodonusage.py b/libcodonusage/libcodonusage.py
index 856af0e8b17effcf9e2db5efa6979394fb012888..309a259810bb689c003b5b1d692cfa4b26ef0af6 100644
--- a/libcodonusage/libcodonusage.py
+++ b/libcodonusage/libcodonusage.py
@@ -14,6 +14,12 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 """Functions used in Jupyter notebooks."""
+
+Some_notes = """
+Good ref is important. Whole genome should be OK, but could be highly expressed genes.
+
+TODO: Try other projections than PCA: manifold learning (for instance t-SNE)...
+"""
 from itertools import chain, combinations
 import json
 from operator import attrgetter, itemgetter