See https://github.com/tscrim/coxeter/pull/15

commit 34484c958bd664e9a2f7578c40d9034dc36386fe
Author: Jeroen Demeyer <jdemeyer@cage.ugent.be>
Date:   Mon Feb 26 15:56:52 2018 +0100

    Remove duplicate declaration of printHeckeElt

diff --git a/files.h b/files.h
index f7bb9db..98a7350 100644
--- a/files.h
+++ b/files.h
@@ -101,10 +101,6 @@ template <class H>
 		     const Interface& I, OutputTraits& traits,
 		     const Length& l = undef_length);
 template <class H>
-  void printHeckeElt(FILE* file, const H& h, const SchubertContext& p,
-		     const Interface& I, OutputTraits& traits,
-		     const Length& l = undef_length);
-template <class H>
   void printHeckeElt(FILE* file, const H& h, const Permutation& a,
 		     const SchubertContext& p, const Interface& I,
 		     HeckeTraits& hTraits,