anchor.diff:        first      =sum
   )
   
  -(p increment-sum
  +(P increment-sum
      =goal>
  -      isa         add
  +      ISA         add
         sum         =sum
         count       =count
       - arg2        =count
      =retrieval>
  -      isa         count-order
  +      ISA         count-order
         first       =sum
         second      =newsum
   ==>
  
positive.code: (p initialize-addition
     =goal>
        isa         add
        arg1        =num1
        arg2        =num2
        sum         nil
  
negative.code:       first      =num1
  )
  
  (P terminate-addition
     =goal>
        ISA         add
        count       =num
        arg2        =num
        sum         =answer
  