diff --git a/lemon/Makefile.am b/lemon/Makefile.am
--- a/lemon/Makefile.am
+++ b/lemon/Makefile.am
@@ -6,14 +6,18 @@
 
 lib_LTLIBRARIES += lemon/libemon.la
 
-lemon_libemon_la_SOURCES =
+lemon_libemon_la_SOURCES = \
+        lemon/base.cc
 
 lemon_libemon_la_CXXFLAGS = $(GLPK_CFLAGS) $(CPLEX_CFLAGS) $(SOPLEX_CXXFLAGS)
 lemon_libemon_la_LDFLAGS = $(GLPK_LIBS) $(CPLEX_LIBS) $(SOPLEX_LIBS)
 
 lemon_HEADERS += \
-	lemon/list_graph.h
+	lemon/list_graph.h \
+        lemon/tolerance.h
 
-bits_HEADERS +=
+bits_HEADERS += \
+        lemon/bits/invalid.h \
+        lemon/bits/utility.h
 
 concept_HEADERS +=
diff --git a/lemon/base.cc b/lemon/base.cc
new file mode 100644
--- /dev/null
+++ b/lemon/base.cc
@@ -0,0 +1,34 @@
+/* -*- C++ -*-
+ *
+ * This file is a part of LEMON, a generic C++ optimization library
+ *
+ * Copyright (C) 2003-2007
+ * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
+ * (Egervary Research Group on Combinatorial Optimization, EGRES).
+ *
+ * Permission to use, modify and distribute this software is granted
+ * provided that this copyright notice appears in all copies. For
+ * precise terms see the accompanying LICENSE file.
+ *
+ * This software is provided "AS IS" with no warranty of any kind,
+ * express or implied, and with no claim as to its suitability for any
+ * purpose.
+ *
+ */
+
+///\file
+///\brief Some basic non inline function and static global data.
+
+#include<lemon/tolerance.h>
+#include<lemon/bits/invalid.h>
+namespace lemon {
+
+  float Tolerance<float>::def_epsilon = 1e-4;
+  double Tolerance<double>::def_epsilon = 1e-10;
+  long double Tolerance<long double>::def_epsilon = 1e-14;
+
+#ifndef LEMON_ONLY_TEMPLATES
+  const Invalid INVALID = Invalid();
+#endif
+
+} //namespace lemon
diff --git a/lemon/bits/invalid.h b/lemon/bits/invalid.h
new file mode 100644
--- /dev/null
+++ b/lemon/bits/invalid.h
@@ -0,0 +1,54 @@
+/* -*- C++ -*-
+ *
+ * This file is a part of LEMON, a generic C++ optimization library
+ *
+ * Copyright (C) 2003-2007
+ * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
+ * (Egervary Research Group on Combinatorial Optimization, EGRES).
+ *
+ * Permission to use, modify and distribute this software is granted
+ * provided that this copyright notice appears in all copies. For
+ * precise terms see the accompanying LICENSE file.
+ *
+ * This software is provided "AS IS" with no warranty of any kind,
+ * express or implied, and with no claim as to its suitability for any
+ * purpose.
+ *
+ */
+
+#ifndef LEMON_BITS_INVALID_H
+#define LEMON_BITS_INVALID_H
+
+///\file
+///\brief Definition of INVALID.
+
+namespace lemon {
+
+  /// \brief Dummy type to make it easier to make invalid iterators.
+  ///
+  /// See \ref INVALID for the usage.
+  struct Invalid {
+  public:
+    bool operator==(Invalid) { return true;  }
+    bool operator!=(Invalid) { return false; }
+    bool operator< (Invalid) { return false; }
+  };
+  
+  /// Invalid iterators.
+  
+  /// \ref Invalid is a global type that converts to each iterator
+  /// in such a way that the value of the target iterator will be invalid.
+
+  //Some people didn't like this:
+  //const Invalid &INVALID = *(Invalid *)0;
+
+#ifdef LEMON_ONLY_TEMPLATES
+  const Invalid INVALID = Invalid();
+#else
+  extern const Invalid INVALID;
+#endif
+
+} //namespace lemon
+
+#endif
+  
diff --git a/lemon/bits/utility.h b/lemon/bits/utility.h
new file mode 100644
--- /dev/null
+++ b/lemon/bits/utility.h
@@ -0,0 +1,140 @@
+/* -*- C++ -*-
+ *
+ * This file is a part of LEMON, a generic C++ optimization library
+ *
+ * Copyright (C) 2003-2007
+ * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
+ * (Egervary Research Group on Combinatorial Optimization, EGRES).
+ *
+ * Permission to use, modify and distribute this software is granted
+ * provided that this copyright notice appears in all copies. For
+ * precise terms see the accompanying LICENSE file.
+ *
+ * This software is provided "AS IS" with no warranty of any kind,
+ * express or implied, and with no claim as to its suitability for any
+ * purpose.
+ *
+ */
+
+// This file contains a modified version of the enable_if library from BOOST.
+// See the appropriate copyright notice below.
+
+// Boost enable_if library
+
+// Copyright 2003 © The Trustees of Indiana University.
+
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+//    Authors: Jaakko Järvi (jajarvi at osl.iu.edu)
+//             Jeremiah Willcock (jewillco at osl.iu.edu)
+//             Andrew Lumsdaine (lums at osl.iu.edu)
+
+
+#ifndef LEMON_BITS_UTILITY_H
+#define LEMON_BITS_UTILITY_H
+
+///\file
+///\brief Miscellaneous basic utilities
+///
+///\todo Please rethink the organisation of the basic files like this.
+///E.g. this file might be merged with invalid.h.
+
+
+namespace lemon
+{
+
+  /// Basic type for defining "tags". A "YES" condition for \c enable_if.
+
+  /// Basic type for defining "tags". A "YES" condition for \c enable_if.
+  ///
+  ///\sa False
+  ///
+  /// \todo This should go to a separate "basic_types.h" (or something)
+  /// file.
+  struct True {
+    ///\e
+    static const bool value = true;
+  };
+
+  /// Basic type for defining "tags". A "NO" condition for \c enable_if.
+
+  /// Basic type for defining "tags". A "NO" condition for \c enable_if.
+  ///
+  ///\sa True
+  struct False {
+    ///\e
+    static const bool value = false;
+  };
+
+
+  struct InvalidType {
+  };
+
+  template <typename T>
+  struct Wrap {
+    const T &value;
+    Wrap(const T &t) : value(t) {}
+  };
+
+  /**************** dummy class to avoid ambiguity ****************/
+
+  template<int T> struct dummy { dummy(int) {} };
+
+  /**************** enable_if from BOOST ****************/
+  
+  template <typename Type, typename T = void>
+  struct exists {
+    typedef T type;
+  };
+
+ 
+  template <bool B, class T = void>
+  struct enable_if_c {
+    typedef T type;
+  };
+
+  template <class T>
+  struct enable_if_c<false, T> {};
+
+  template <class Cond, class T = void> 
+  struct enable_if : public enable_if_c<Cond::value, T> {};
+
+  template <bool B, class T>
+  struct lazy_enable_if_c {
+    typedef typename T::type type;
+  };
+
+  template <class T>
+  struct lazy_enable_if_c<false, T> {};
+
+  template <class Cond, class T> 
+  struct lazy_enable_if : public lazy_enable_if_c<Cond::value, T> {};
+
+
+  template <bool B, class T = void>
+  struct disable_if_c {
+    typedef T type;
+  };
+
+  template <class T>
+  struct disable_if_c<true, T> {};
+
+  template <class Cond, class T = void> 
+  struct disable_if : public disable_if_c<Cond::value, T> {};
+
+  template <bool B, class T>
+  struct lazy_disable_if_c {
+    typedef typename T::type type;
+  };
+
+  template <class T>
+  struct lazy_disable_if_c<true, T> {};
+
+  template <class Cond, class T> 
+  struct lazy_disable_if : public lazy_disable_if_c<Cond::value, T> {};
+
+} // namespace lemon
+
+#endif
diff --git a/lemon/tolerance.h b/lemon/tolerance.h
new file mode 100644
--- /dev/null
+++ b/lemon/tolerance.h
@@ -0,0 +1,454 @@
+/* -*- C++ -*-
+ *
+ * This file is a part of LEMON, a generic C++ optimization library
+ *
+ * Copyright (C) 2003-2007
+ * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
+ * (Egervary Research Group on Combinatorial Optimization, EGRES).
+ *
+ * Permission to use, modify and distribute this software is granted
+ * provided that this copyright notice appears in all copies. For
+ * precise terms see the accompanying LICENSE file.
+ *
+ * This software is provided "AS IS" with no warranty of any kind,
+ * express or implied, and with no claim as to its suitability for any
+ * purpose.
+ *
+ */
+
+#ifndef LEMON_TOLERANCE_H
+#define LEMON_TOLERANCE_H
+
+///\ingroup misc
+///\file
+///\brief A basic tool to handle the anomalies of calculation with
+///floating point numbers.
+///
+///\todo It should be in a module like "Basic tools"
+
+
+namespace lemon {
+
+  /// \addtogroup misc
+  /// @{
+  
+  ///\brief A class to provide a basic way to
+  ///handle the comparison of numbers that are obtained
+  ///as a result of a probably inexact computation.
+  ///
+  ///Tolerance is a class to provide a basic way to
+  ///handle the comparison of numbers that are obtained
+  ///as a result of a probably inexact computation.
+  ///
+  ///This is an abstract class, it should be specialized for all numerical
+  ///data types. These specialized classes like \ref Tolerance\<double\>
+  ///may offer additional tuning parameters.
+  ///
+  ///\sa Tolerance<float>
+  ///\sa Tolerance<double>
+  ///\sa Tolerance<long double>
+  ///\sa Tolerance<int>
+  ///\sa Tolerance<long long int>
+  ///\sa Tolerance<unsigned int>
+  ///\sa Tolerance<unsigned long long int>
+
+  template<class T>
+  class Tolerance
+  {
+  public:
+    typedef T Value;
+
+    ///\name Comparisons
+    ///The concept is that these bool functions return with \c true only if
+    ///the related comparisons hold even if some numerical error appeared
+    ///during the computations.
+
+    ///@{
+
+    ///Returns \c true if \c a is \e surely strictly less than \c b
+    static bool less(Value a,Value b) {return false;}
+    ///Returns \c true if \c a is \e surely different from \c b
+    static bool different(Value a,Value b) {return false;}
+    ///Returns \c true if \c a is \e surely positive
+    static bool positive(Value a) {return false;}
+    ///Returns \c true if \c a is \e surely negative
+    static bool negative(Value a) {return false;}
+    ///Returns \c true if \c a is \e surely non-zero
+    static bool nonZero(Value a) {return false;}
+
+    ///@}
+
+    ///Returns the zero value.
+    static Value zero() {return T();}
+
+    //   static bool finite(Value a) {}
+    //   static Value big() {}
+    //   static Value negativeBig() {}
+  };
+
+
+  ///Float specialization of \ref Tolerance.
+
+  ///Float specialization of \ref Tolerance.
+  ///\sa Tolerance
+  ///\relates Tolerance
+  template<>
+  class Tolerance<float>
+  {
+    static float def_epsilon;
+    float _epsilon;
+  public:
+    ///\e
+    typedef float Value;
+
+    ///Constructor setting the epsilon tolerance to the default value.
+    Tolerance() : _epsilon(def_epsilon) {}
+    ///Constructor setting the epsilon tolerance.
+    Tolerance(float e) : _epsilon(e) {}
+
+    ///Return the epsilon value.
+    Value epsilon() const {return _epsilon;}
+    ///Set the epsilon value.
+    void epsilon(Value e) {_epsilon=e;}
+
+    ///Return the default epsilon value.
+    static Value defaultEpsilon() {return def_epsilon;}
+    ///Set the default epsilon value.
+    static void defaultEpsilon(Value e) {def_epsilon=e;}
+
+    ///\name Comparisons
+    ///See class Tolerance for more details.
+
+    ///@{
+
+    ///Returns \c true if \c a is \e surely strictly less than \c b
+    bool less(Value a,Value b) const {return a+_epsilon<b;}
+    ///Returns \c true if \c a is \e surely different from \c b
+    bool different(Value a,Value b) const { return less(a,b)||less(b,a); }
+    ///Returns \c true if \c a is \e surely positive
+    bool positive(Value a) const { return _epsilon<a; }
+    ///Returns \c true if \c a is \e surely negative
+    bool negative(Value a) const { return -_epsilon>a; }
+    ///Returns \c true if \c a is \e surely non-zero
+    bool nonZero(Value a) const { return positive(a)||negative(a); };
+
+    ///@}
+
+    ///Returns zero
+    static Value zero() {return 0;}
+  };
+
+  ///Double specialization of \ref Tolerance.
+
+  ///Double specialization of \ref Tolerance.
+  ///\sa Tolerance
+  ///\relates Tolerance
+  template<>
+  class Tolerance<double>
+  {
+    static double def_epsilon;
+    double _epsilon;
+  public:
+    ///\e
+    typedef double Value;
+
+    ///Constructor setting the epsilon tolerance to the default value.
+    Tolerance() : _epsilon(def_epsilon) {}
+    ///Constructor setting the epsilon tolerance.
+    Tolerance(double e) : _epsilon(e) {}
+
+    ///Return the epsilon value.
+    Value epsilon() const {return _epsilon;}
+    ///Set the epsilon value.
+    void epsilon(Value e) {_epsilon=e;}
+
+    ///Return the default epsilon value.
+    static Value defaultEpsilon() {return def_epsilon;}
+    ///Set the default epsilon value.
+    static void defaultEpsilon(Value e) {def_epsilon=e;}
+
+    ///\name Comparisons
+    ///See class Tolerance for more details.
+
+    ///@{
+
+    ///Returns \c true if \c a is \e surely strictly less than \c b
+    bool less(Value a,Value b) const {return a+_epsilon<b;}
+    ///Returns \c true if \c a is \e surely different from \c b
+    bool different(Value a,Value b) const { return less(a,b)||less(b,a); }
+    ///Returns \c true if \c a is \e surely positive
+    bool positive(Value a) const { return _epsilon<a; }
+    ///Returns \c true if \c a is \e surely negative
+    bool negative(Value a) const { return -_epsilon>a; }
+    ///Returns \c true if \c a is \e surely non-zero
+    bool nonZero(Value a) const { return positive(a)||negative(a); };
+
+    ///@}
+
+    ///Returns zero
+    static Value zero() {return 0;}
+  };
+
+  ///Long double specialization of \ref Tolerance.
+
+  ///Long double specialization of \ref Tolerance.
+  ///\sa Tolerance
+  ///\relates Tolerance
+  template<>
+  class Tolerance<long double>
+  {
+    static long double def_epsilon;
+    long double _epsilon;
+  public:
+    ///\e
+    typedef long double Value;
+
+    ///Constructor setting the epsilon tolerance to the default value.
+    Tolerance() : _epsilon(def_epsilon) {}
+    ///Constructor setting the epsilon tolerance.
+    Tolerance(long double e) : _epsilon(e) {}
+
+    ///Return the epsilon value.
+    Value epsilon() const {return _epsilon;}
+    ///Set the epsilon value.
+    void epsilon(Value e) {_epsilon=e;}
+
+    ///Return the default epsilon value.
+    static Value defaultEpsilon() {return def_epsilon;}
+    ///Set the default epsilon value.
+    static void defaultEpsilon(Value e) {def_epsilon=e;}
+
+    ///\name Comparisons
+    ///See class Tolerance for more details.
+
+    ///@{
+
+    ///Returns \c true if \c a is \e surely strictly less than \c b
+    bool less(Value a,Value b) const {return a+_epsilon<b;}
+    ///Returns \c true if \c a is \e surely different from \c b
+    bool different(Value a,Value b) const { return less(a,b)||less(b,a); }
+    ///Returns \c true if \c a is \e surely positive
+    bool positive(Value a) const { return _epsilon<a; }
+    ///Returns \c true if \c a is \e surely negative
+    bool negative(Value a) const { return -_epsilon>a; }
+    ///Returns \c true if \c a is \e surely non-zero
+    bool nonZero(Value a) const { return positive(a)||negative(a); };
+
+    ///@}
+
+    ///Returns zero
+    static Value zero() {return 0;}
+  };
+
+  ///Integer specialization of \ref Tolerance.
+
+  ///Integer specialization of \ref Tolerance.
+  ///\sa Tolerance
+  template<>
+  class Tolerance<int>
+  {
+  public:
+    ///\e
+    typedef int Value;
+
+    ///\name Comparisons
+    ///See \ref Tolerance for more details.
+
+    ///@{
+
+    ///Returns \c true if \c a is \e surely strictly less than \c b
+    static bool less(Value a,Value b) { return a<b;}
+    ///Returns \c true if \c a is \e surely different from \c b
+    static bool different(Value a,Value b) { return a!=b; }
+    ///Returns \c true if \c a is \e surely positive
+    static bool positive(Value a) { return 0<a; }
+    ///Returns \c true if \c a is \e surely negative
+    static bool negative(Value a) { return 0>a; }
+    ///Returns \c true if \c a is \e surely non-zero
+    static bool nonZero(Value a) { return a!=0; };
+
+    ///@}
+
+    ///Returns zero
+    static Value zero() {return 0;}
+  };
+
+  ///Unsigned integer specialization of \ref Tolerance.
+
+  ///Unsigned integer specialization of \ref Tolerance.
+  ///\sa Tolerance
+  template<>
+  class Tolerance<unsigned int>
+  {
+  public:
+    ///\e
+    typedef unsigned int Value;
+
+    ///\name Comparisons
+    ///See \ref Tolerance for more details.
+
+    ///@{
+
+    ///Returns \c true if \c a is \e surely strictly less than \c b
+    static bool less(Value a,Value b) { return a<b;}
+    ///Returns \c true if \c a is \e surely different from \c b
+    static bool different(Value a,Value b) { return a!=b; }
+    ///Returns \c true if \c a is \e surely positive
+    static bool positive(Value a) { return 0<a; }
+    ///Returns \c true if \c a is \e surely negative
+    static bool negative(Value) { return false; }
+    ///Returns \c true if \c a is \e surely non-zero
+    static bool nonZero(Value a) { return a!=0; };
+
+    ///@}
+
+    ///Returns zero
+    static Value zero() {return 0;}
+  };
+  
+
+  ///Long integer specialization of \ref Tolerance.
+
+  ///Long integer specialization of \ref Tolerance.
+  ///\sa Tolerance
+  template<>
+  class Tolerance<long int>
+  {
+  public:
+    ///\e
+    typedef long int Value;
+
+    ///\name Comparisons
+    ///See \ref Tolerance for more details.
+
+    ///@{
+
+    ///Returns \c true if \c a is \e surely strictly less than \c b
+    static bool less(Value a,Value b) { return a<b;}
+    ///Returns \c true if \c a is \e surely different from \c b
+    static bool different(Value a,Value b) { return a!=b; }
+    ///Returns \c true if \c a is \e surely positive
+    static bool positive(Value a) { return 0<a; }
+    ///Returns \c true if \c a is \e surely negative
+    static bool negative(Value a) { return 0>a; }
+    ///Returns \c true if \c a is \e surely non-zero
+    static bool nonZero(Value a) { return a!=0;};
+
+    ///@}
+
+    ///Returns zero
+    static Value zero() {return 0;}
+  };
+
+  ///Unsigned long integer specialization of \ref Tolerance.
+
+  ///Unsigned long integer specialization of \ref Tolerance.
+  ///\sa Tolerance
+  template<>
+  class Tolerance<unsigned long int>
+  {
+  public:
+    ///\e
+    typedef unsigned long int Value;
+
+    ///\name Comparisons
+    ///See \ref Tolerance for more details.
+
+    ///@{
+
+    ///Returns \c true if \c a is \e surely strictly less than \c b
+    static bool less(Value a,Value b) { return a<b;}
+    ///Returns \c true if \c a is \e surely different from \c b
+    static bool different(Value a,Value b) { return a!=b; }
+    ///Returns \c true if \c a is \e surely positive
+    static bool positive(Value a) { return 0<a; }
+    ///Returns \c true if \c a is \e surely negative
+    static bool negative(Value) { return false; }
+    ///Returns \c true if \c a is \e surely non-zero
+    static bool nonZero(Value a) { return a!=0;};
+
+    ///@}
+
+    ///Returns zero
+    static Value zero() {return 0;}
+  };
+
+#if defined __GNUC__ && !defined __STRICT_ANSI__
+
+  ///Long long integer specialization of \ref Tolerance.
+
+  ///Long long integer specialization of \ref Tolerance.
+  ///\warning This class (more exactly, type <tt>long long</tt>)
+  ///is not ansi compatible.
+  ///\sa Tolerance
+  template<>
+  class Tolerance<long long int>
+  {
+  public:
+    ///\e
+    typedef long long int Value;
+
+    ///\name Comparisons
+    ///See \ref Tolerance for more details.
+
+    ///@{
+
+    ///Returns \c true if \c a is \e surely strictly less than \c b
+    static bool less(Value a,Value b) { return a<b;}
+    ///Returns \c true if \c a is \e surely different from \c b
+    static bool different(Value a,Value b) { return a!=b; }
+    ///Returns \c true if \c a is \e surely positive
+    static bool positive(Value a) { return 0<a; }
+    ///Returns \c true if \c a is \e surely negative
+    static bool negative(Value a) { return 0>a; }
+    ///Returns \c true if \c a is \e surely non-zero
+    static bool nonZero(Value a) { return a!=0;};
+
+    ///@}
+
+    ///Returns zero
+    static Value zero() {return 0;}
+  };
+
+  ///Unsigned long long integer specialization of \ref Tolerance.
+
+  ///Unsigned long long integer specialization of \ref Tolerance.
+  ///\warning This class (more exactly, type <tt>unsigned long long</tt>)
+  ///is not ansi compatible.
+  ///\sa Tolerance
+  template<>
+  class Tolerance<unsigned long long int>
+  {
+  public:
+    ///\e
+    typedef unsigned long long int Value;
+
+    ///\name Comparisons
+    ///See \ref Tolerance for more details.
+
+    ///@{
+
+    ///Returns \c true if \c a is \e surely strictly less than \c b
+    static bool less(Value a,Value b) { return a<b;}
+    ///Returns \c true if \c a is \e surely different from \c b
+    static bool different(Value a,Value b) { return a!=b; }
+    ///Returns \c true if \c a is \e surely positive
+    static bool positive(Value a) { return 0<a; }
+    ///Returns \c true if \c a is \e surely negative
+    static bool negative(Value) { return false; }
+    ///Returns \c true if \c a is \e surely non-zero
+    static bool nonZero(Value a) { return a!=0;};
+
+    ///@}
+
+    ///Returns zero
+    static Value zero() {return 0;}
+  };
+
+#endif
+
+  /// @}
+
+} //namespace lemon
+
+#endif //LEMON_TOLERANCE_H