Add copyright headers

Author: Matthias Koeppe

src/sage/symbolic/expression_conversion_algebraic.py

@@ -1,6 +1,21 @@
 r"""
 Conversion of symbolic expressions to algebraic numbers
 """
+# ****************************************************************************
+#       Copyright (C) 2009-2012 Mike Hansen
+#                     2015-2018 Ralf Stephan
+#                     2015      Nils Bruin
+#                     2017      Jeroen Demeyer
+#                     2019-2022 Frédéric Chapoton
+#                     2021      Dave Witte Morris
+#                     2023      Vincent Delecroix
+#
+# 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 2 of the License, or
+# (at your option) any later version.
+#                  https://www.gnu.org/licenses/
+# ****************************************************************************
 
 from operator import eq, ne, gt, lt, ge, le, mul, pow, neg, add, truediv
 from functools import reduce

src/sage/symbolic/expression_conversion_sympy.py

@@ -2,6 +2,20 @@
 r"""
 Conversion of symbolic expressions to SymPy
 """
+# ****************************************************************************
+#       Copyright (C) 2009 Mike Hansen
+#                     2011 D. S. McNeil
+#                     2011 Francois Bissey
+#                     2017 Ralf Stephan
+#                     2017 Marco Mancini
+#                     2017 Travis Scrimshaw
+#
+# 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 2 of the License, or
+# (at your option) any later version.
+#                  https://www.gnu.org/licenses/
+# ****************************************************************************
 
 from operator import eq, ne, gt, lt, ge, le, mul, pow, neg, add, truediv
 

src/sage/symbolic/symbols.py

@@ -1,3 +1,16 @@
+r"""
+Symbol table
+"""
+# ****************************************************************************
+#       Copyright (C) 2009 Mike Hansen
+#
+# 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 2 of the License, or
+# (at your option) any later version.
+#                  https://www.gnu.org/licenses/
+# ****************************************************************************
+
 symbol_table = {'functions': {}}