Referenced objects should not be deep copied

In expressions that are in function calls are deep copies of the expression of the relevant function definition. This is performed right after instantiation of the model in a model processor. This deepcopy relies in turn on the __deepcopy__ method specified here.

The problem is that variables that are referenced are also copied. This leads to variables in the expressions that have the same names as the original but not children of the model because they are only referenced and not integral part of any object, see model diagram below. Therefore these variable copies do not have the attributes aquired after the model processor has run. This is a problem for the implementation of the persistent dynamic model.