code: public void pop(GraphicalModel model) {
              assert(model.factors.contains(addedFactor));
              model.factors.remove(addedFactor);
              model.getVariableMetaDataByReference(variable).remove(CliqueTree.VARIABLE_OBSERVED_VALUE);
          }
docs: See push() for an explanation.
  
  @param model the model to pop this SampleState from