Problem in tutorial with new interaction Implementation

Hello, first of all, thanks a lot to Steffen for the tutorial regarding coding new interactions. It contains a lot of information I've missed. As I copied everything from ElasticInteraction, I did also a ElasticInteractionGroup (that seems not neccesary, and other things probably wrong).
Nevertheless, I have the development code, so it has yet the HertzianInteraction yet. I compiled the code, and the problem is that when I try to run an example, I have the same error than with my own interaction:

File "two_particles.py", line 51, in <module>
    HertzianElasticPrms(
NameError: name 'HertzianElasticPrms' is not defined

So, the problem probably is how I do the calling. Probably is something so evident that I can not see it. The code in the script that calls the interaction is:

sim.createInteractionGroup(
   HertzianElasticPrms(
      name = "HertzSpheres",
      YoungE = 10000.0,
   nu = 0.3
   )
)

The name HertzianElasticPrms is what appears in the export function:

      boost::python::class_<HertzianElasticPrmsPy,boost::python::bases<InteractionPrmsPy> >(
        "HertzianElasticPrms",
        "Parameters for Hertzian elastic contact interactions.",
        boost::python::init<const std::string &, double, double>(
          (
            arg("name"),
            arg("E"),
     arg("nu")
          ),
          "@type name: string\n"
          "@kwarg name: Name assigned to this group of interactions.\n"
          "@type E: float\n"
          "@kwarg E: Young's modulus used for force calculation.\n"
          "@type nu: float\n"
          "@kwarg nu: poisson ratio used for force calculation.\n"
        )
      )
      .def(
        "getName",
        &HertzianElasticPrmsPy::getName,
        boost::python::return_value_policy<boost::python::copy_const_reference>()
      )
      ;
I've checked the Makefile to see if it's included in the libraries, and it is. So, I can not see where is the error.

Thanks in advance and best regards,