diff --git a/hdxrate/psx/IntrinsicExchange.py b/hdxrate/psx/IntrinsicExchange.py
index 55a4b27..09825c7 100644
--- a/hdxrate/psx/IntrinsicExchange.py
+++ b/hdxrate/psx/IntrinsicExchange.py
@@ -1,3 +1,19 @@
+"""
+Copyright 2019, University of Copenhagen
+
+Martin Cramer Pedersen, mcpe@nbi.ku.dk
+
+This file is part of PSX.
+
+PSX 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.
+
+PSX 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.
+
+You should have received a copy of the GNU General Public License along with PSX. If not, see http://www.gnu.org/licenses/.
+"""
+
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 # Imports #
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