code: public List<Literal> perceive() {
          if (!isRunning())
              return null;
          if (this.getSimulation() == null)
              return null;
          List<Literal> percepts = this.updateBeliefs(this.getSimulation());
          return percepts;
      }
docs: /*
  (non-Javadoc)
  
  @see jason.architecture.AgArch#perceive()