anchor.diff:     either a StreamSelect or SingleSelect object."
     (is-term (list +term-term-type-table+
                    +term-term-type-get+
  +                 +term-term-type-var+
                    +term-term-type-get-all+
                    +term-term-type-between+
                    +term-term-type-filter+)
  
positive.code:                      +term-term-type-outer-join+
                       +term-term-type-eq-join+
                       +term-term-type-zip+
                       +term-term-type-funcall+
                       +term-term-type-branch+)
                 object)
  
negative.code:       (is-boolean object)
        (is-term (list +term-term-type-default+
                       +term-term-type-match+
                       +term-term-type-var+
                       +term-term-type-coerce-to+)
                 object)))
  
  