diff --git a/src/TOOLS/invert.irp.f b/src/TOOLS/invert.irp.f
index 0c8e3a3..73d4b0a 100644
--- a/src/TOOLS/invert.irp.f
+++ b/src/TOOLS/invert.irp.f
@@ -1,3 +1,45 @@
+! This file contains the fast inversion routines of QMC=Chem for
+! small matrices. It may be downloaded here:
+! https://raw.githubusercontent.com/scemama/qmcchem/master/src/TOOLS/invert.irp.f
+! 
+! To use it in your Fortran code, you will need to~:
+! 1) rename it inverse.f90
+! 2) replace all $IRP_ALIGN occurences by 
+!    a) 16  for SSE4.2
+!    b) 32  for AVX or AVX2
+!    c) 64  for AVX-512
+!
+!
+! GPL license :
+! -------------
+!
+!   QMC=Chem : Quantum Monte Carlo for Chemistry
+!   Copyright (C) 2009 Anthony SCEMAMA 
+!
+!   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.
+!
+!   This program 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 this program; if not, write to the Free Software Foundation, Inc.,
+!   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+!
+!   Anthony Scemama
+!   LCPQ - IRSAMC - CNRS
+!   Universite Paul Sabatier
+!   118, route de Narbonne      
+!   31062 Toulouse Cedex 4      
+!   scemama@irsamc.ups-tlse.fr
+!
+!
+
+
 subroutine invert(a,LDA,na,det_l)
  implicit none
  double precision, intent(inout) :: a (LDA,na)