The TypeTree library, headers and test programs are copyrighted free software. You can use, modify and/or redistribute it under the terms of either one of the two following licenses:
The GNU Lesser General Public License as published by the Free Software Foundation, either Version 3 of the license or (at your option) any later version. You can find a copy of the GNU Lesser General Public License, Version 3, in the files GPL-3 and LGPL-3 or at http://www.gnu.org/licenses/lgpl-3.0.
Version 2 of the GNU General Public License as published by the Free Software Foundation, with the following special exception for linking and compiling against the TypeTree library, the so-called “runtime exception”:
As a special exception, you may use the PDELab source files as part of a software library or application without restriction. Specifically, if other files instantiate templates or use macros or inline functions from one or more of the PDELab source files, or you compile one or more of the PDELab source files and link them with other files to produce an executable, this does not by itself cause the resulting executable to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the executable file might be covered by the GNU General Public License.
This license is intended to be similar to the GNU Lesser General Public License, Version 2, which by itself isn’t suitable for a template library. You can find a copy of the GNU General Public License, Version 2, in the file GPL-2 or at http://www.gnu.org/licenses/gpl-2.0.