diff --git a/exercice_4/README.md b/exercice_4/README.md
index 59944d2..6cc11c0 100644
--- a/exercice_4/README.md
+++ b/exercice_4/README.md
@@ -1,40 +1,41 @@
 # Readme exercice 4
 
 code by Marti Bosch (marti.bosch@epfl.ch) and Marc Schwaerzel (marc.schwaerzel@epfl.ch) 
 
 ## Exercise 1
 
 ## Exercise 2
 2.2 We used shared pointers for the pybind of the classes compute and compute_temperature in order not to desallocate when python's reference count goes to 0. A unique pointer could lead to a segmentation fault (memory allocation issues).
-2.3 We used the method where we put setters directely in the compute_temperature.py in order to access private members from outside the class.But there is a smarter way to access private members --> reread class notes and implement them
+2.3 We used the method where we put setters directely in the compute_temperature.py in order to access private members from outside the class.But there is a smarter way to access private members --> reread class notes and implement them.
 
 ## Exercise 3
-In this exercice we need to write csvwrite in the pybind with the given name.
-We also need to create setter for evol.setNsteps, evol.setDumpFreq, evol.evolve
+created bind for csvwriter, evol.setNsteps, evol.setDumpFreq and evol.evolve...
+
+still need something for     self.system_evolution.addCompute(compute_temp) ln50 of main
 
 
 ## Instructions to run the code
 
 To run the code follow the instructions:
 
 1) Create a new directory in the exercice_4 directory and go into that folder:
 	
 	$ mkdir build
 	$ cd build
 
 2) Check whether your paths are set correctly
 
 	$ ccmake ../
 
 2) Compile the code:
 	
 	$ cmake ../
 	$ make
 
 3) Then run as follows
 
 	$ ./particles --help
     
     Usage: ./particles nsteps dump_freq input.csv particle_type timestep
 	    particle type can be: planet, ping_pong, material_point
 
diff --git a/exercice_4/src/pypart_pybind.cc b/exercice_4/src/pypart_pybind.cc
index effd784..2bf982c 100644
--- a/exercice_4/src/pypart_pybind.cc
+++ b/exercice_4/src/pypart_pybind.cc
@@ -1,56 +1,63 @@
 #include "material_points_factory.hh"
 #include "particles_factory_interface.hh"
 #include "ping_pong_balls_factory.hh"
 #include "planets_factory.hh"
 #include "compute_temperature.hh"
 #include "csv_writer.hh"
 #include <pybind11/pybind11.h>
 
 namespace py = pybind11;
 
 PYBIND11_MODULE(pypart, m) {
   m.doc() = "pybind for particles code";
 
   py::class_<ParticlesFactoryInterface>(m, "ParticlesFactoryInterface")
       .def("getInstance", &ParticlesFactoryInterface::getInstance)
       .def("createSimulation", &ParticlesFactoryInterface::createSimulation);
 
   py::class_<MaterialPointsFactory, ParticlesFactoryInterface>(
       m, "MaterialPointsFactory")
       .def("getInstance", &MaterialPointsFactory::getInstance)
       /*.def("createSimulation", py::overload_cast<const std::string &, Real>(
                                    &MaterialPointsFactory::createSimulation))
       // no need for py::overload_cast<const std::string &, Real, py::function>
       .def("createSimulation",
            py::overload_cast<const std::string &, Real, py::function>(
                &MaterialPointsFactory::createSimulation<py::function>));
       */
       .def("createSimulation", // less elegant way to do the overload cast --> forum
 	   (SystemEvolution& (MaterialPointsFactory::*)(const std::string &, Real)) &          		MaterialPointsFactory::createSimulation
 	   );  
   py::class_<PingPongBallsFactory, ParticlesFactoryInterface>(
       m, "PingPongBallsFactory")
       .def("getInstance", &PingPongBallsFactory::getInstance)
       .def("createSimulation", &PingPongBallsFactory::createSimulation);
 
   py::class_<PlanetsFactory, ParticlesFactoryInterface>(m, "PlanetsFactory")
       .def("getInstance", &PlanetsFactory::getInstance)
       .def("createSimulation", &PlanetsFactory::createSimulation);
 
   py::class_<Compute, std::shared_ptr<Compute>>(m, "Compute");
 
   py::class_<ComputeTemperature, Compute, std::shared_ptr<ComputeTemperature>
 	     >(m, "ComputeTemperature")
     .def("compute", &ComputeTemperature::compute)
     .def_property("conductivity", &ComputeTemperature::setConductivity,
 		  &ComputeTemperature::getConductivity)
     .def_property("capacity", &ComputeTemperature::setCapacity, &ComputeTemperature::getCapacity)
     .def_property("density", &ComputeTemperature::setDensity, &ComputeTemperature::getDensity)
     .def_property("L", &ComputeTemperature::setL, &ComputeTemperature::getL)
     .def_property("delta_t", &ComputeTemperature::setDeltat, &ComputeTemperature::getDeltat);
 
   py::class_<CsvWriter, Compute, std::shared_ptr<CsvWriter>>(m, "CsvWriter")
     .def(py::init<const std::string&>())
-    .def("write", &CsvWriter::write)
-    ;
+    .def("write", &CsvWriter::write);
+
+  py::class_<System>(m, "System");
+
+  py::class_<SystemEvolution>(m, "SystemEvolution")
+    .def("setNSteps", &SystemEvolution::setNSteps)
+    .def("setDumpFreq", &SystemEvolution::setDumpFreq)
+    .def("evolve", &SystemEvolution::evolve);
+
 }