diff --git a/LICENSE.rst b/LICENSE.rst
index f374800da8ec53fdf8f3a8323b6bfae07aeed37c..a5b574905fd0edee0a262dc71cbc72ca0b05e2c8 100644
--- a/LICENSE.rst
+++ b/LICENSE.rst
@@ -1,5 +1,5 @@
-GNU GENERAL PUBLIC LICENSE
-~~~~~~~~~~~~~~~~~~~~~~~~~~
+GNU LESSER GENERAL PUBLIC LICENSE
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Version 3, 29 June 2007
 
@@ -8,698 +8,164 @@ Copyright (C) 2007 Free Software Foundation, Inc. https://fsf.org/
 Everyone is permitted to copy and distribute verbatim copies of this
 license document, but changing it is not allowed.
 
+This version of the GNU Lesser General Public License incorporates the
+terms and conditions of version 3 of the GNU General Public License,
+supplemented by the additional permissions listed below.
 
-Preamble
-~~~~~~~~
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-THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME
-THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
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-16. Limitation of Liability.
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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-WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR
-CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
-INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES
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-WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
-ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
-
-17. Interpretation of Sections 15 and 16.
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-If the disclaimer of warranty and limitation of liability provided above
-cannot be given local legal effect according to their terms, reviewing
-courts shall apply local law that most closely approximates an absolute
-waiver of all civil liability in connection with the Program, unless a
-warranty or assumption of liability accompanies a copy of the Program in
-return for a fee.
-
-END OF TERMS AND CONDITIONS
-
-
-How to Apply These Terms to Your New Programs
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-If you develop a new program, and you want it to be of the greatest
-possible use to the public, the best way to achieve this is to make it
-free software which everyone can redistribute and change under these
-terms.
+As used herein, "this License" refers to version 3 of the GNU Lesser
+General Public License, and the "GNU GPL" refers to version 3 of the GNU
+General Public License.
 
-To do so, attach the following notices to the program. It is safest to
-attach them to the start of each source file to most effectively state
-the exclusion of warranty; and each file should have at least the
-"copyright" line and a pointer to where the full notice is found.
+"The Library" refers to a covered work governed by this License, other
+than an Application or a Combined Work as defined below.
 
-::
+An "Application" is any work that makes use of an interface provided by
+the Library, but which is not otherwise based on the Library. Defining a
+subclass of a class defined by the Library is deemed a mode of using an
+interface provided by the Library.
 
-    <one line to give the program's name and a brief idea of what it does.>
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+which the Combined Work was made is also called the "Linked Version".
 
-    This program is free software: you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
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+The "Minimal Corresponding Source" for a Combined Work means the
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-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
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-    GNU General Public License for more details.
+The "Corresponding Application Code" for a Combined Work means the
+object code and/or source code for the Application, including any data
+and utility programs needed for reproducing the Combined Work from the
+Application, but excluding the System Libraries of the Combined Work.
 
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-Also add information on how to contact you by electronic and paper mail.
-
-If the program does terminal interaction, make it output a short notice
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-The hypothetical commands \`show w' and \`show c' should show the
-appropriate parts of the General Public License. Of course, your
-program's commands might be different; for a GUI interface, you would
-use an "about box".
+1. Exception to Section 3 of the GNU GPL.
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-You should also get your employer (if you work as a programmer) or
-school, if any, to sign a "copyright disclaimer" for the program, if
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-GNU GPL, see https://www.gnu.org/licenses/.
+You may convey a covered work under sections 3 and 4 of this License
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+
+2. Conveying Modified Versions.
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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+If you modify a copy of the Library, and, in your modifications, a
+facility refers to a function or data to be supplied by an Application
+that uses the facility (other than as an argument passed when the
+facility is invoked), then you may convey a copy of the modified
+version:
+
+   a) under this License, provided that you make a good faith effort to
+      ensure that, in the event an Application does not supply the
+      function or data, the facility still operates, and performs
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+
+   b) under the GNU GPL, with none of the additional permissions of this
+      License applicable to that copy.
+
+3. Object Code Incorporating Material from Library Header Files.
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The object code form of an Application may incorporate material from a
+header file that is part of the Library. You may convey such object code
+under terms of your choice, provided that, if the incorporated material
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+lines in length), you do both of the following:
+
+   a) Give prominent notice with each copy of the object code that the
+      Library is used in it and that the Library and its use are covered
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+      license document.
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+4. Combined Works.
+^^^^^^^^^^^^^^^^^^
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+together, effectively do not restrict modification of the portions of
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+      copies of the GNU GPL and this license document.
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+   d) Do one of the following:
+
+      0) Convey the Minimal Corresponding Source under the terms of this
+         License, and the Corresponding Application Code in a form
+         suitable for, and under terms that permit, the user to
+         recombine or relink the Application with a modified version of
+         the Linked Version to produce a modified Combined Work, in the
+         manner specified by section 6 of the GNU GPL for conveying
+         Corresponding Source.
+
+      1) Use a suitable shared library mechanism for linking with the
+         Library. A suitable mechanism is one that (a) uses at run time
+         a copy of the Library already present on the user's computer
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+         of the Library that is interface-compatible with the Linked
+         Version.
+
+   e) Provide Installation Information, but only if you would otherwise
+      be required to provide such information under section 6 of the GNU
+      GPL, and only to the extent that such information is necessary to
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+      the Installation Information must accompany the Minimal
+      Corresponding Source and Corresponding Application Code. If you
+      use option 4d1, you must provide the Installation Information in
+      the manner specified by section 6 of the GNU GPL for conveying
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+5. Combined Libraries.
+^^^^^^^^^^^^^^^^^^^^^^
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+side by side in a single library together with other library facilities
+that are not Applications and are not covered by this License, and
+convey such a combined library under terms of your choice, if you do
+both of the following:
+
+   a) Accompany the combined library with a copy of the same work based
+      on the Library, uncombined with any other library facilities,
+      conveyed under the terms of this License.
+
+   b) Give prominent notice with the combined library that part of it is
+      a work based on the Library, and explaining where to find the
+      accompanying uncombined form of the same work.
+
+6. Revised Versions of the GNU Lesser General Public License.
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-The GNU General Public License does not permit incorporating your
-program into proprietary programs. If your program is a subroutine
-library, you may consider it more useful to permit linking proprietary
-applications with the library. If this is what you want to do, use the
-GNU Lesser General Public License instead of this License. But first,
-please read https://www.gnu.org/philosophy/why-not-lgpl.html.
+The Free Software Foundation may publish revised and/or new versions of
+the GNU Lesser General Public License from time to time. Such new
+versions will be similar in spirit to the present version, but may
+differ in detail to address new problems or concerns.
+
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+you received it specifies that a certain numbered version of the GNU
+Lesser General Public License "or any later version" applies to it, you
+have the option of following the terms and conditions either of that
+published version or of any later version published by the Free Software
+Foundation. If the Library as you received it does not specify a version
+number of the GNU Lesser General Public License, you may choose any
+version of the GNU Lesser General Public License ever published by the
+Free Software Foundation.
+
+If the Library as you received it specifies that a proxy can decide
+whether future versions of the GNU Lesser General Public License shall
+apply, that proxy's public statement of acceptance of any version is
+permanent authorization for you to choose that version for the Library.
diff --git a/README.rst b/README.rst
index 780b5c465f18062126d1712d7f1259d1e223f67c..6fa615db1009aaec420a47708bc36e0a6c7efbff 100644
--- a/README.rst
+++ b/README.rst
@@ -12,7 +12,7 @@ useful when writing schedulers.
 Features
 --------
 
-- Free Software: licensed under GPLv3+ (see `<LICENSE.rst>`_).
+- Free Software: licensed under LGPLv3 (see `<LICENSE.rst>`_).
 - Pure Python module :)
 - Thoroughly tested!
 - Drop-in replacement for `interval_set` (see `intsetwrap.py
diff --git a/setup.cfg b/setup.cfg
index 8ebe66ce5c06ba65a6edb863e2d3f8ed92061d22..e28bf42fd0f3a646ef0af63602dfe8828c91b5c4 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -16,7 +16,7 @@ classifiers =
     Development Status :: 2 - Pre-Alpha
     Intended Audience :: Developers
     Intended Audience :: Science/Research
-    License :: OSI Approved :: GNU General Public License v3 or later (GPLv3+)
+    License :: OSI Approved :: GNU Lesser General Public License v3 (LGPLv3)
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3.5
     Topic :: Software Development :: Libraries :: Python Modules
diff --git a/src/intsetwrap.py b/src/intsetwrap.py
index a33ddbfb64d2413c4c0eb70de9fa3cf58da0fe84..dc04914f442393d7b15bbf6000a48234bb0d20ea 100644
--- a/src/intsetwrap.py
+++ b/src/intsetwrap.py
@@ -3,18 +3,21 @@
 # Copyright © 2017
 # Contributed by Raphaël Bleuse <raphael.bleuse@imag.fr>
 #
-#   This program is free software: you can redistribute it and/or modify
-#   it under the terms of the GNU General Public License as published by
-#   the Free Software Foundation, either version 3 of the License, or
-#   (at your option) any later version.
+# This file is part of procset.py, a pure python module to manage sets of
+# closed intervals.
 #
-#   This program is distributed in the hope that it will be useful,
+#   procset.py is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU Lesser General Public License version 3 only
+#   as published by the Free Software Foundation.
+#
+#   procset.py is distributed in the hope that it will be useful,
 #   but WITHOUT ANY WARRANTY; without even the implied warranty of
 #   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-#   GNU General Public License for more details.
+#   GNU Lesser General Public License version 3 for more details.
 #
-#   You should have received a copy of the GNU General Public License
-#   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#   You should have received a copy of the GNU Lesser General Public
+#   License version 3 along with this program.  If not, see
+#   <https://www.gnu.org/licenses/>.
 
 """
 Wrapper functions around procset to provide the API of interval_set.
diff --git a/src/procset.py b/src/procset.py
index e32cee91e254c757b3762f7450e89bc03f6034c0..925ff0cb93b077954dea538659ec07034b133e7f 100644
--- a/src/procset.py
+++ b/src/procset.py
@@ -3,18 +3,21 @@
 # Copyright © 2017
 # Contributed by Raphaël Bleuse <raphael.bleuse@imag.fr>
 #
-#   This program is free software: you can redistribute it and/or modify
-#   it under the terms of the GNU General Public License as published by
-#   the Free Software Foundation, either version 3 of the License, or
-#   (at your option) any later version.
+# This file is part of procset.py, a pure python module to manage sets of
+# closed intervals.
 #
-#   This program is distributed in the hope that it will be useful,
+#   procset.py is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU Lesser General Public License version 3 only
+#   as published by the Free Software Foundation.
+#
+#   procset.py is distributed in the hope that it will be useful,
 #   but WITHOUT ANY WARRANTY; without even the implied warranty of
 #   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-#   GNU General Public License for more details.
+#   GNU Lesser General Public License version 3 for more details.
 #
-#   You should have received a copy of the GNU General Public License
-#   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#   You should have received a copy of the GNU Lesser General Public
+#   License version 3 along with this program.  If not, see
+#   <https://www.gnu.org/licenses/>.
 
 """
 Toolkit to manage sets of closed intervals.
diff --git a/test/test_procint.py b/test/test_procint.py
index b9be7c0761a842413c20962a364498b8929d6426..bf04f034efc2e5d9e559ecb4b802f6f94844647c 100644
--- a/test/test_procint.py
+++ b/test/test_procint.py
@@ -3,18 +3,21 @@
 # Copyright © 2017
 # Contributed by Raphaël Bleuse <raphael.bleuse@imag.fr>
 #
-#   This program is free software: you can redistribute it and/or modify
-#   it under the terms of the GNU General Public License as published by
-#   the Free Software Foundation, either version 3 of the License, or
-#   (at your option) any later version.
+# This file is part of procset.py, a pure python module to manage sets of
+# closed intervals.
 #
-#   This program is distributed in the hope that it will be useful,
+#   procset.py is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU Lesser General Public License version 3 only
+#   as published by the Free Software Foundation.
+#
+#   procset.py is distributed in the hope that it will be useful,
 #   but WITHOUT ANY WARRANTY; without even the implied warranty of
 #   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-#   GNU General Public License for more details.
+#   GNU Lesser General Public License version 3 for more details.
 #
-#   You should have received a copy of the GNU General Public License
-#   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#   You should have received a copy of the GNU Lesser General Public
+#   License version 3 along with this program.  If not, see
+#   <https://www.gnu.org/licenses/>.
 
 import pytest
 from procset import ProcInt
diff --git a/test/test_procset.py b/test/test_procset.py
index 89b44a1e0a1596d3836df6a3fa6b7046f079129f..d64674f2d96d548b9fa82d48aa2031a6caa08b82 100644
--- a/test/test_procset.py
+++ b/test/test_procset.py
@@ -3,18 +3,21 @@
 # Copyright © 2017
 # Contributed by Raphaël Bleuse <raphael.bleuse@imag.fr>
 #
-#   This program is free software: you can redistribute it and/or modify
-#   it under the terms of the GNU General Public License as published by
-#   the Free Software Foundation, either version 3 of the License, or
-#   (at your option) any later version.
+# This file is part of procset.py, a pure python module to manage sets of
+# closed intervals.
 #
-#   This program is distributed in the hope that it will be useful,
+#   procset.py is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU Lesser General Public License version 3 only
+#   as published by the Free Software Foundation.
+#
+#   procset.py is distributed in the hope that it will be useful,
 #   but WITHOUT ANY WARRANTY; without even the implied warranty of
 #   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-#   GNU General Public License for more details.
+#   GNU Lesser General Public License version 3 for more details.
 #
-#   You should have received a copy of the GNU General Public License
-#   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#   You should have received a copy of the GNU Lesser General Public
+#   License version 3 along with this program.  If not, see
+#   <https://www.gnu.org/licenses/>.
 
 import pytest
 from procset import ProcInt, ProcSet
diff --git a/test/test_procset_set_operations.py b/test/test_procset_set_operations.py
index 9f6655ee149294f5abb641abaf0b164332d59734..bc263f67e1db6cff75e4c01eba6f5176b4b3857d 100644
--- a/test/test_procset_set_operations.py
+++ b/test/test_procset_set_operations.py
@@ -3,18 +3,21 @@
 # Copyright © 2017
 # Contributed by Raphaël Bleuse <raphael.bleuse@imag.fr>
 #
-#   This program is free software: you can redistribute it and/or modify
-#   it under the terms of the GNU General Public License as published by
-#   the Free Software Foundation, either version 3 of the License, or
-#   (at your option) any later version.
+# This file is part of procset.py, a pure python module to manage sets of
+# closed intervals.
 #
-#   This program is distributed in the hope that it will be useful,
+#   procset.py is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU Lesser General Public License version 3 only
+#   as published by the Free Software Foundation.
+#
+#   procset.py is distributed in the hope that it will be useful,
 #   but WITHOUT ANY WARRANTY; without even the implied warranty of
 #   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-#   GNU General Public License for more details.
+#   GNU Lesser General Public License version 3 for more details.
 #
-#   You should have received a copy of the GNU General Public License
-#   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#   You should have received a copy of the GNU Lesser General Public
+#   License version 3 along with this program.  If not, see
+#   <https://www.gnu.org/licenses/>.
 
 
 # The naming convention of the tests follows the one in the position paper by
diff --git a/test/test_wrapper.py b/test/test_wrapper.py
index b01e0b5eb444efc50070f51f8a0228d1171c84ec..7ac9a6bf391d868d28db5d6337dac107a51959ea 100644
--- a/test/test_wrapper.py
+++ b/test/test_wrapper.py
@@ -3,18 +3,21 @@
 # Copyright © 2017
 # Contributed by Raphaël Bleuse <raphael.bleuse@imag.fr>
 #
-#   This program is free software: you can redistribute it and/or modify
-#   it under the terms of the GNU General Public License as published by
-#   the Free Software Foundation, either version 3 of the License, or
-#   (at your option) any later version.
+# This file is part of procset.py, a pure python module to manage sets of
+# closed intervals.
 #
-#   This program is distributed in the hope that it will be useful,
+#   procset.py is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU Lesser General Public License version 3 only
+#   as published by the Free Software Foundation.
+#
+#   procset.py is distributed in the hope that it will be useful,
 #   but WITHOUT ANY WARRANTY; without even the implied warranty of
 #   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-#   GNU General Public License for more details.
+#   GNU Lesser General Public License version 3 for more details.
 #
-#   You should have received a copy of the GNU General Public License
-#   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#   You should have received a copy of the GNU Lesser General Public
+#   License version 3 along with this program.  If not, see
+#   <https://www.gnu.org/licenses/>.
 
 import pytest
 import interval_set.interval_set as oldapi