diff --git a/eo/test/Makefile.am b/eo/test/Makefile.am
index 33124b50..604922de 100644
--- a/eo/test/Makefile.am
+++ b/eo/test/Makefile.am
@@ -18,7 +18,7 @@ noinst_PROGRAMS = t-eobreeder t-eoinclusion t-eoinsertion t-eo t-eofitness \
 	t-eoproblem t-eobin t-eolottery t-eo2dVector t-eogeneration t-eoEasyEA\
 	t-eoNonUniform t-eoUniform t-eoRandom t-eoStateAndParser \
 	t-eoAtomOps t-selectOne t-eoGOpSel \
-	t-eoVector t-eoCheckpointing
+	t-eoVector t-eoCheckpointing t-eoExternalEO
 
 ###############################################################################
 
@@ -170,3 +170,12 @@ t_eoCheckpointing_LDFLAGS = -lm
 t_eoCheckpointing_LDADD = $(LDADDS) 
 
 ###############################################################################
+
+t_eoExternalEO_SOURCES = t-eoCheckpointing.cpp
+t_eoExternalEO_DEPENDENCIES = $(DEPS) 
+t_eoExternalEO_LDFLAGS = -lm 
+t_eoExternalEO_LDADD = $(LDADDS) 
+
+###############################################################################
+
+
diff --git a/eo/test/t-eoCheckpointing.cpp b/eo/test/t-eoCheckpointing.cpp
index ee4ac0a9..742c357a 100644
--- a/eo/test/t-eoCheckpointing.cpp
+++ b/eo/test/t-eoCheckpointing.cpp
@@ -75,28 +75,46 @@ int the_main(int argc, char **argv)
 
     eoDummyPop pop;
     
-    eoGenTerm<EoType> genTerm(5); // 5 generations
+    eoGenTerm<EoType> genTerm(5); // run for 5 generations
 
-    eoCheckPoint<EoType> checkpoint(genTerm);
+    eoCheckPoint<EoType> checkpoint(genTerm); 
+    // The algorithm will now quit after five generations
 
+    // Create a counter parameter
     eoValueParam<unsigned> generationCounter(0, "Generation");
+    
+    // Create an incrementor (wich is an eoUpdater). Note that the 
+    // Parameter's value is passed by reference, so every time the incrementer increments,
+    // the data in generationCounter will change.
     eoIncrementor<unsigned> increment(generationCounter.value());
 
+    // Add it to the checkpoint, this will result in the counter being incremented every generation
     checkpoint.add(increment);
 
+    // The file monitor will print parameters to a comma seperated file
     eoFileMonitor monitor("monitor.csv");
+    
+    // the checkpoint mechanism can handle multiple monitors
     checkpoint.add(monitor);
 
+    // the monitor can monitor parameters such as the generationCounter
     monitor.add(generationCounter);
 
+    // Second moment stats: average and stdev
     eoSecondMomentStats<EoType> stats;
 
+    // Add it to the checkpoint to get it called at the appropriate time
     checkpoint.add(stats);
+
+    // Add it to the monitor to get it written to the file
     monitor.add(stats);
 
-    eoCountedStateSaver stateSaver1(3, state, "generation"); // save every third generation
-    eoTimedStateSaver   stateSaver2(2, state, "time"); // save every 2 seconds
+    // save state every third generation
+    eoCountedStateSaver stateSaver1(3, state, "generation"); 
+    // save state every 2 seconds 
+    eoTimedStateSaver   stateSaver2(2, state, "time"); 
 
+    // And add the two savers to the checkpoint
     checkpoint.add(stateSaver1);
     checkpoint.add(stateSaver2);
 
@@ -150,11 +168,6 @@ int the_main(int argc, char **argv)
         state.save(file_name);
     }
 
-    for (int i = 0; i < 100; ++i)
-        rng.rand();
-
-    cout << "a random number is " << rng.random(1024) << endl;;
-
     return 1;
 }
 
diff --git a/eo/test/t-eoExternalEO.cpp b/eo/test/t-eoExternalEO.cpp
new file mode 100644
index 00000000..d750280e
--- /dev/null
+++ b/eo/test/t-eoExternalEO.cpp
@@ -0,0 +1,127 @@
+// to avoid long name warnings
+#ifdef _MSC_VER
+#pragma warning(disable:4786)
+#endif
+
+#include <iostream>
+#include <stdexcept>  // runtime_error 
+
+#include <eoEvalFuncPtr.h>
+#include <other/external_eo>
+#include <utils/eoRNG.h>
+
+using namespace std;
+
+struct UserDefStruct
+{
+    int a;
+    float b;
+    double c;
+    enum Enum { just, another, test } d;
+};
+
+ostream& operator<<(ostream& os, const UserDefStruct& str)
+{
+    return os << str.a << ' ' << str.b << ' ' << str.c << ' ' << static_cast<int>(str.d) << ' ';
+}
+
+istream& operator>>(istream& is, UserDefStruct& str)
+{
+    is >> str.a;
+    is >> str.b;
+    is >> str.c;
+    int i;
+    is >> i;
+    str.d = static_cast<UserDefStruct::Enum>(i);
+
+    return is;
+}
+
+
+UserDefStruct RandomStruct()
+{
+    cout << "RandomStruct\n";
+
+    UserDefStruct result;
+
+    result.a = rng.random(5);
+    result.b = rng.uniform();
+    result.c = rng.uniform();
+    result.d = UserDefStruct::another;
+
+    return result;
+}
+
+// reading and writing
+
+
+void UserDefMutate(UserDefStruct& a)
+{
+    cout << "UserDefMutate\n";
+    a = RandomStruct(); // just for testing
+
+    if (rng.flip(0.1f))
+        a.d = UserDefStruct::test;
+    else
+        a.d = UserDefStruct::another;
+}
+
+void UserDefBinCrossover(UserDefStruct& a, const UserDefStruct& b)
+{
+    cout << "UserDefBinCrossover\n";
+
+    if (rng.flip(0.5))
+        a.a = b.a;
+    if (rng.flip(0.5))
+        a.b = b.b;
+    if (rng.flip(0.5))
+        a.c = b.c;
+    if (rng.flip(0.5))
+        a.d = b.d;
+}
+
+void UserDefQuadCrossover(UserDefStruct& a, UserDefStruct& b)
+{
+    cout << "UserDefQuadCrossover\n";
+    if (rng.flip(0.5))
+        swap(a.a, b.a);
+    if (rng.flip(0.5))
+        swap(a.b, b.b);
+    if (rng.flip(0.5))
+        swap(a.c, b.c);
+    if (rng.flip(0.5))
+        swap(a.d, b.d);
+}
+
+float UserDefEvalFunc(const UserDefStruct& a)
+{
+    cout << "UserDefEvalFunc\n";
+    return a.b;
+}
+
+int main()
+{
+    typedef UserDefStruct External;
+    typedef float FitnessType;
+    typedef eoExternalEO<float, External> EoType;
+
+    eoExternalInit<FitnessType, External> init(RandomStruct);
+    eoExternalMonOp<FitnessType, External> mutate(UserDefMutate);
+    eoExternalBinOp<FitnessType, External> cross1(UserDefBinCrossover);
+    eoExternalQuadraticOp<FitnessType, External> cross2(UserDefQuadCrossover);
+
+    eoExternalEvalFunc<FitnessType, External>   eval(UserDefEvalFunc);
+
+    EoType eo1 = init();
+    EoType eo2 = init();
+
+    cout << "before mutation " << eo1 << '\n';
+    mutate(eo1);
+    cout << "after mutation " << eo1 << '\n';
+    cross1(eo1, eo2);
+    cout << "after crossover " << eo1 << '\n';
+
+    cross2(eo1,eo2);
+
+    return 1;
+};
\ No newline at end of file
diff --git a/eo/test/t-eofitness.cpp b/eo/test/t-eofitness.cpp
index f3161620..9973444a 100644
--- a/eo/test/t-eofitness.cpp
+++ b/eo/test/t-eofitness.cpp
@@ -1,87 +1,175 @@
-//-----------------------------------------------------------------------------
-// t-eofitness.cpp
-// (c) GeNeura Team 1998
-//-----------------------------------------------------------------------------
-
-#include <time.h>    // time
-#include <stdlib.h>  // srand, rand
-#include <iostream>  // cout
-#include <eo>        // eoFitness
-
-//-----------------------------------------------------------------------------
-
-class eoFloat: public eoFitness
-{
-public:
-  eoFloat(const float x) { fitness = x; }
-  eoFloat(const int x) { fitness = static_cast<float>(x); }
-
-  bool operator<(const eoFitness& other) const
-    {
-      const eoFloat& x = (const eoFloat&) other;
-      return fitness < x.fitness;
-    }
-
-  operator float() const
-    {
-      return fitness;
-    }
-
-  void printOn(ostream& os) const
-    {
-      os << fitness;
-    }
-  
-  void readFrom(istream& is)
-    {
-      is >> fitness;
-    }
-
-private:
-  float fitness;
-};
-
-//-----------------------------------------------------------------------------
-
-main()
-{
-  srand(time(0));
-
-  eoFloat a = static_cast<float>(rand()) / RAND_MAX, 
-    b = static_cast<float>(rand()) / RAND_MAX;
-
-  cout.precision(2);
-  
-  unsigned repeat = 2;
-  while (repeat--)
-    {
-      cout << "------------------------------------------------------" << endl;
-      cout << "testing <    ";
-      if (a < b)
-	cout << a << " < " << b << "  is true" << endl;
-      else
-	cout << a << " < " << b << "  is false" <<endl;
-      
-      cout << "testing >    ";
-      if (a > b)
-	cout << a << " > " << b << "  is true" << endl;
-      else
-	cout << a << " > " << b << "  is false" <<endl;
-      
-      cout << "testing ==   ";
-      if (a == b)
-	cout << a << " == " << b << " is true" << endl;
-      else
-	cout << a << " == " << b << " is false" <<endl;
-      
-      cout << "testing !=   ";
-      if (a != b)
-	cout << a << " != " << b << " is true" << endl;
-      else
-	cout << a << " != " << b << " is false" <<endl;
-      
-      a = b;
-    }
-}
-
-//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+// t-eofitness.cpp
+
+// (c) GeNeura Team 1998
+
+//-----------------------------------------------------------------------------
+
+
+
+#include <time.h>    // time
+
+#include <stdlib.h>  // srand, rand
+
+#include <iostream>  // cout
+
+#include <eo>        // eoFitness
+
+
+
+//-----------------------------------------------------------------------------
+
+
+
+class eoFloat: public eoFitness
+
+{
+
+public:
+
+  eoFloat(const float x) { fitness = x; }
+
+  eoFloat(const int x) { fitness = static_cast<float>(x); }
+
+
+
+  bool operator<(const eoFitness& other) const
+
+    {
+
+      const eoFloat& x = (const eoFloat&) other;
+
+      return fitness < x.fitness;
+
+    }
+
+
+
+  operator float() const
+
+    {
+
+      return fitness;
+
+    }
+
+
+
+  void printOn(ostream& os) const
+
+    {
+
+      os << fitness;
+
+    }
+
+  
+
+  void readFrom(istream& is)
+
+    {
+
+      is >> fitness;
+
+    }
+
+
+
+private:
+
+  float fitness;
+
+};
+
+
+
+//-----------------------------------------------------------------------------
+
+
+
+int main()
+
+{
+
+  srand(time(0));
+
+
+
+  eoFloat a = static_cast<float>(rand()) / RAND_MAX, 
+
+    b = static_cast<float>(rand()) / RAND_MAX;
+
+
+
+  cout.precision(2);
+
+  
+
+  unsigned repeat = 2;
+
+  while (repeat--)
+
+    {
+
+      cout << "------------------------------------------------------" << endl;
+
+      cout << "testing <    ";
+
+      if (a < b)
+
+	cout << a << " < " << b << "  is true" << endl;
+
+      else
+
+	cout << a << " < " << b << "  is false" <<endl;
+
+      
+
+      cout << "testing >    ";
+
+      if (a > b)
+
+	cout << a << " > " << b << "  is true" << endl;
+
+      else
+
+	cout << a << " > " << b << "  is false" <<endl;
+
+      
+
+      cout << "testing ==   ";
+
+      if (a == b)
+
+	cout << a << " == " << b << " is true" << endl;
+
+      else
+
+	cout << a << " == " << b << " is false" <<endl;
+
+      
+
+      cout << "testing !=   ";
+
+      if (a != b)
+
+	cout << a << " != " << b << " is true" << endl;
+
+      else
+
+	cout << a << " != " << b << " is false" <<endl;
+
+      
+
+      a = b;
+
+    }
+
+  return 1;
+}
+
+
+
+//-----------------------------------------------------------------------------
+
diff --git a/eo/test/t-eoproblem.cpp b/eo/test/t-eoproblem.cpp
index 05265204..e7c36666 100644
--- a/eo/test/t-eoproblem.cpp
+++ b/eo/test/t-eoproblem.cpp
@@ -36,7 +36,7 @@ const unsigned Easy::size = 1;
 
 //-----------------------------------------------------------------------------
 
-main()
+int main()
 {
   Easy easy;
   Chrom chrom(Easy::size);
@@ -48,6 +48,8 @@ main()
   
   cout << "chrom = " << chrom << endl
        << "chrom.fitness() = " << chrom.fitness() << endl;
+
+  return 0;
 }
 
 //-----------------------------------------------------------------------------