anchor.diff:                Body = { Position = v2Zero; LinearVelocity = v2Zero; Rotation = 0.0f; AngularVelocity = 0.0f; Gravity = v2 0.0f -9.81f }
                 Image = image
                 Rate = rate
  -              Id = Gen.id }+              Id = Gen.id }
  
positive.code: 
          /// Run the emitter.
          abstract Run : int64 -> Constraint -> Emitter * Output
  
      /// Transforms a particle value.
      type 'a Transformer =
  
negative.code:             member this.Run time constrain =
                  let (emitter, output) = Emitter<'a>.run time constrain this
                  (emitter :> Emitter, output)
              member this.ToParticlesDescriptor time =
                  this.ToParticlesDescriptor time this
              end
  
      /// A particle system.
  