anchor.diff: -(p initialize-addition
  +(define-model addition
  +
  +(chunk-type count-order first second)
  +(chunk-type add arg1 arg2 sum count)
  +
  +(add-dm
  +   (a ISA count-order first 0 second 1)
  +   (b ISA count-order first 1 second 2)
  +   (c ISA count-order first 2 second 3)
  +   (d ISA count-order first 3 second 4)
  +   (e ISA count-order first 4 second 5)
  +   (f ISA count-order first 5 second 6)
  +   (g ISA count-order first 6 second 7)
  +   (h ISA count-order first 7 second 8)
  +   (i ISA count-order first 8 second 9)
  +   (j ISA count-order first 9 second 10)
  +   (second-goal ISA add arg1 5 arg2 2))
  +
  +(P initialize-addition
      =goal>
  -      isa         add
  +      ISA         add
         arg1        =num1
         arg2        =num2
         sum         nil
  
positive.code:       first      =sum
  )
  
  (p increment-sum
     =goal>
        isa         add
        sum         =sum
        count       =count
      - arg2        =count
     =retrieval>
        isa         count-order
        first       =sum
        second      =newsum
  ==>
  
negative.code:       count       nil
  )
  
  (P increment-count
     =goal>
        ISA         add
        sum         =sum
        count       =count
     =retrieval>
        ISA         count-order
        first       =count
        second      =newcount
  ==>
  