diff --git a/lemon/glpk.h b/lemon/glpk.h
--- a/lemon/glpk.h
+++ b/lemon/glpk.h
@@ -26,9 +26,10 @@
 #include <lemon/lp_base.h>
 
 // forward declaration
-#ifndef _GLP_PROB
+#if !defined _GLP_PROB && !defined GLP_PROB
 #define _GLP_PROB
-typedef struct { double _prob; } glp_prob;
+#define GLP_PROB
+typedef struct { double _opaque_prob; } glp_prob;
 /* LP/MIP problem object */
 #endif
 
@@ -53,6 +54,7 @@
 
     virtual int _addCol();
     virtual int _addRow();
+    virtual int _addRow(Value l, ExprIterator b, ExprIterator e, Value u);
 
     virtual void _eraseCol(int i);
     virtual void _eraseRow(int i);
@@ -100,6 +102,24 @@
 
     virtual void _clear();
 
+    virtual void _messageLevel(MessageLevel level);
+
+  private:
+
+    static void freeEnv();
+
+    struct FreeEnvHelper {
+      ~FreeEnvHelper() {
+        freeEnv();
+      }
+    };
+    
+    static FreeEnvHelper freeEnvHelper;
+
+  protected:
+    
+    int _message_level;
+    
   public:
 
     ///Pointer to the underlying GLPK data structure.
@@ -119,7 +139,7 @@
   ///
   /// This class implements an interface for the GLPK LP solver.
   ///\ingroup lp_group
-  class GlpkLp : public GlpkBase, public LpSolver {
+  class GlpkLp : public LpSolver, public GlpkBase {
   public:
 
     ///\e
@@ -127,6 +147,11 @@
     ///\e
     GlpkLp(const GlpkLp&);
 
+    ///\e
+    virtual GlpkLp* cloneSolver() const;
+    ///\e
+    virtual GlpkLp* newSolver() const;
+
   private:
 
     mutable std::vector<double> _primal_ray;
@@ -136,9 +161,6 @@
 
   protected:
 
-    virtual GlpkLp* _cloneSolver() const;
-    virtual GlpkLp* _newSolver() const;
-
     virtual const char* _solverName() const;
 
     virtual SolveExitStatus _solve();
@@ -153,8 +175,6 @@
     virtual Value _getPrimalRay(int i) const;
     virtual Value _getDualRay(int i) const;
 
-    ///\todo It should be clarified
-    ///
     virtual ProblemType _getPrimalType() const;
     virtual ProblemType _getDualType() const;
 
@@ -166,44 +186,26 @@
     ///Solve with dual simplex
     SolveExitStatus solveDual();
 
+  private:
+
+    bool _presolve;
+
+  public:
+
     ///Turns on or off the presolver
 
     ///Turns on (\c b is \c true) or off (\c b is \c false) the presolver
     ///
     ///The presolver is off by default.
-    void presolver(bool b);
+    void presolver(bool presolve);
 
-    ///Enum for \c messageLevel() parameter
-    enum MessageLevel {
-      /// no output (default value)
-      MESSAGE_NO_OUTPUT = 0,
-      /// error messages only
-      MESSAGE_ERROR_MESSAGE = 1,
-      /// normal output
-      MESSAGE_NORMAL_OUTPUT = 2,
-      /// full output (includes informational messages)
-      MESSAGE_FULL_OUTPUT = 3
-    };
-
-  private:
-
-    MessageLevel _message_level;
-
-  public:
-
-    ///Set the verbosity of the messages
-
-    ///Set the verbosity of the messages
-    ///
-    ///\param m is the level of the messages output by the solver routines.
-    void messageLevel(MessageLevel m);
   };
 
   /// \brief Interface for the GLPK MIP solver
   ///
   /// This class implements an interface for the GLPK MIP solver.
   ///\ingroup lp_group
-  class GlpkMip : public GlpkBase, public MipSolver {
+  class GlpkMip : public MipSolver, public GlpkBase {
   public:
 
     ///\e
@@ -211,11 +213,11 @@
     ///\e
     GlpkMip(const GlpkMip&);
 
+    virtual GlpkMip* cloneSolver() const;
+    virtual GlpkMip* newSolver() const;
+
   protected:
 
-    virtual GlpkMip* _cloneSolver() const;
-    virtual GlpkMip* _newSolver() const;
-
     virtual const char* _solverName() const;
 
     virtual ColTypes _getColType(int col) const;
@@ -226,30 +228,6 @@
     virtual Value _getSol(int i) const;
     virtual Value _getSolValue() const;
 
-    ///Enum for \c messageLevel() parameter
-    enum MessageLevel {
-      /// no output (default value)
-      MESSAGE_NO_OUTPUT = 0,
-      /// error messages only
-      MESSAGE_ERROR_MESSAGE = 1,
-      /// normal output
-      MESSAGE_NORMAL_OUTPUT = 2,
-      /// full output (includes informational messages)
-      MESSAGE_FULL_OUTPUT = 3
-    };
-
-  private:
-
-    MessageLevel _message_level;
-
-  public:
-
-    ///Set the verbosity of the messages
-
-    ///Set the verbosity of the messages
-    ///
-    ///\param m is the level of the messages output by the solver routines.
-    void messageLevel(MessageLevel m);
   };