anchor.diff:  /**
    * Base class for all physical behaviour, forces and constraint effectors.
    */
  -abstract class Effector 
  +abstract class Effector<P extends Particle> 
   {
     prepare() {}
  -  apply(Particle p);
  +  apply(P p);
   }
   
   abstract class Behaviour extends Effector {}
  
positive.code:   
    Physics() {
      space = new BasicSpace(this);
      emitter = new Emitter(this); 
    }
    
    addEffector(Effector effector, [int state=Particle.ALIVE]) {
  
negative.code: class Physics<P extends Particle, S extends Spring>
  {  
    Space space;
    Emitter<P> emitter;
    List<P> particles = [];
    List<S> springs = [];
    
  