https://bugs.gentoo.org/686484

polyhedralfan.h: At global scope:
polyhedralfan.h:77:24: error: friend declaration of ‘PolyhedralFan refinement(const PolyhedralFan&, const PolyhedralFan&, int, bool)’ specifies default arguments and isn’t a definition [-fpermissive]
   77 |   friend PolyhedralFan refinement(const PolyhedralFan &a, const PolyhedralFan &b, int cutOffDimension=-1, bool allowASingleConeOfCutOffDimension=false);
      |                        ^~~~~~~~~~

--- a/gfanlib_polyhedralfan.h
+++ b/gfanlib_polyhedralfan.h
@@ -24,6 +24,8 @@
 typedef std::map<int,IntVectorList> IncidenceList;
 
 
+class PolyhedralFan;
+PolyhedralFan refinement(const PolyhedralFan &a, const PolyhedralFan &b, int cutOffDimension=-1, bool allowASingleConeOfCutOffDimension=false);
 
 /** A PolyhedralFan is simply a collection of canonicalized PolyhedralCones.
  * It contains no combinatorial information in the sense of a polyhedral complex.
@@ -52,7 +54,7 @@
   int getAmbientDimension()const;
   int getMaxDimension()const;
   int getMinDimension()const;
-  friend PolyhedralFan refinement(const PolyhedralFan &a, const PolyhedralFan &b, int cutOffDimension=-1, bool allowASingleConeOfCutOffDimension=false);
+  friend PolyhedralFan refinement(const PolyhedralFan &a, const PolyhedralFan &b, int cutOffDimension, bool allowASingleConeOfCutOffDimension);
   ZMatrix getRays(int dim=1);//This can be called for other dimensions than 1. The term "Rays" still makes sense modulo the common linearity space
   ZMatrix getRelativeInteriorPoints();
   void insert(ZCone const &c);
--- a/halfopencone.h
+++ b/halfopencone.h
@@ -6,6 +6,9 @@
 
 #include "polyhedralfan.h"
 
+class HalfOpenCone;
+HalfOpenCone intersection(const HalfOpenCone &a, const HalfOpenCone &b, bool findFacets=false);
+
 class HalfOpenCone{
   static void appendList(IntegerVectorList &to, IntegerVectorList const &from, int appendValue);
   int liftedDimension;//ambient
@@ -18,7 +21,7 @@
   HalfOpenCone(int dimension_, IntegerVectorList const &equations, IntegerVectorList const &nonstrict, IntegerVectorList const &strict, bool findFacets=false, bool canonicalize=false);
   HalfOpenCone(int ambientDimension);//full space
   bool isEmpty();
-  friend HalfOpenCone intersection(const HalfOpenCone &a, const HalfOpenCone &b, bool findFacets=false);
+  friend HalfOpenCone intersection(const HalfOpenCone &a, const HalfOpenCone &b, bool findFacets);
   friend bool haveEmptyIntersection(const HalfOpenCone &a, const HalfOpenCone &b);
   PolyhedralCone closure();
   void splitIntoRelativelyOpenCones(list<HalfOpenCone> &l);
--- a/polyhedralfan.h
+++ b/polyhedralfan.h
@@ -30,6 +30,8 @@
   FPF_default=2+4+8
 };
 
+class PolyhedralFan;
+PolyhedralFan refinement(const PolyhedralFan &a, const PolyhedralFan &b, int cutOffDimension=-1, bool allowASingleConeOfCutOffDimension=false);
 
 /** A PolyhedralFan is simply a collection of canonicalized PolyhedralCones.
  * It contains no combinatorial information in the sense of a polyhedral complex.
@@ -74,7 +76,7 @@
   int getAmbientDimension()const;
   int getMaxDimension()const;
   int getMinDimension()const;
-  friend PolyhedralFan refinement(const PolyhedralFan &a, const PolyhedralFan &b, int cutOffDimension=-1, bool allowASingleConeOfCutOffDimension=false);
+  friend PolyhedralFan refinement(const PolyhedralFan &a, const PolyhedralFan &b, int cutOffDimension, bool allowASingleConeOfCutOffDimension);
   friend PolyhedralFan product(const PolyhedralFan &a, const PolyhedralFan &b);
   IntegerVectorList getRays(int dim=1);//This can be called for other dimensions than 1. The term "Rays" still makes sense modulo the common linearity space
   IntegerVectorList getRelativeInteriorPoints();