anchor.diff:             :used-external-functions
              :ast
              :function-asts
  +           :to-arg-form
  +           :uniform-variables
   
              ;;utils
              :map-environments
  
positive.code:            :find-mutual-cast-type
             :v-special-functionp
             :v-errorp
  
             ;;type accessors
             :core-typep
  
negative.code:            :v-casts-to-p
             :v-casts-to
             :find-mutual-cast-type
             :name
  
             ;;type functions
             :type-specp
  