anchor.diff:          ;; Default initform when type is missing:
           nil)))
   
  -(defun nil-fallback-type-zero-function (definition)
  +(defun nil-fallback-initform-inference (definition)
     "Infer basic type zero values.
   Fall back to nil if initform is missing for unsupported types."
     (let ((type (definition-type definition)))
  
positive.code:         ;; Default initform when type is missing:
          nil)))
  
  (defun no-unbound-type-zero-function (definition)
    "Infer basic type zero values.
  Raise a condition when instantiating if initform is missing for unsupported types."
    (let ((type (definition-type definition)))
  
negative.code:     ((subtypep type 'number) 0.0)
      (t (error "Unknown type"))))
  
  (defun type-zero-initform-inference (definition)
    "Infer basic type zero values.
  See `basic-type-zero-values'.
  Raise a condition at macro-expansion time when initform is missing for unsupported types."
  