code: def explicit_singular_entities(self, tax_benefit_system, input_dict):
          
  
          singular_keys = set(input_dict).intersection(tax_benefit_system.entities_by_singular())
          if not singular_keys:
              return input_dict
  
          result = {
              entity_id: entity_description
              for (entity_id, entity_description) in input_dict.items()
              if entity_id in tax_benefit_system.entities_plural()
              }  # filter out the singular entities
  
          for singular in singular_keys:
              plural = tax_benefit_system.entities_by_singular()[singular].plural
              result[plural] = {singular: input_dict[singular]}
  
          return result
docs: Preprocess ``input_dict`` to explicit entities defined using the single-entity shortcut
  
              Example:
  
              >>> simulation_builder.explicit_singular_entities(
                  {'persons': {'Javier': {}, }, 'household': {'parents': ['Javier']}}
                  )
              >>> {'persons': {'Javier': {}}, 'households': {'household': {'parents': ['Javier']}}