anchor.diff:                       +term-term-type-mul+
                        +term-term-type-div+
                        +term-term-type-mod+
  +                     +term-term-type-get-field+
                        +term-term-type-count+
                        +term-term-type-var+
                        +term-term-type-funcall+
  
positive.code:       (is-function object)
        (is-term (list +term-term-type-add+
                       +term-term-type-var+
                       +term-term-type-funcall+
                       +term-term-type-branch+)
                 object)))
  
negative.code:                      +term-term-type-gt+
                       +term-term-type-ge+
                       +term-term-type-not+
                       +term-term-type-get-field+
                       +term-term-type-contains+
                       +term-term-type-is-empty+
                       +term-term-type-has-fields+
  