anchor.diff:  		 (return-from %presentation-typep t)))
          sequence)
     nil)
  +
  +;;; Useful for subtype comparisons for several of the "member" style types
  +
  +(defun sequence-subset-p (seq1 test1 value-key1 seq2 test2 value-key2)
  +  (let ((test-fun (if (eq test1 test2)
  +		      test1
  +		      ;; The object has to pass both type's equality test
  +		      #'(lambda (obj1 obj2)
  +			  (and (funcall test1 obj1 obj2)
  +			       (funcall test2 obj1 obj2))))))
  +    (map nil #'(lambda (type-obj)
  +		 (unless (find (funcall value-key1 type-obj)
  +			       seq2
  +			       :test test-fun :key value-key2)
  +		   (return-from sequence-subset-p nil)))
  +	 seq1)
  +    t))
  +
  +(define-presentation-method presentation-subtypep ((type completion)
  +						   maybe-supertype)
  +  (with-presentation-type-parameters (completion maybe-supertype)
  +    (let ((super-sequence sequence)
  +	  (super-test test)
  +	  (super-value-key value-key))
  +      (with-presentation-type-parameters (completion type)
  +	(values (sequence-subset-p sequence test value-key
  +				   super-sequence super-test super-value-key)
  +		t)))))
   
   (define-presentation-type-abbreviation member (&rest elements)
     (make-presentation-type-specifier `(completion ,elements)
  
positive.code: 	  (return-from presentation-typep (typep object name)))))
      (funcall-presentation-generic-function presentation-typep object type)))
  
  ;;; The presentation types
  
  (define-presentation-type t ())
  
negative.code:        (or (eq high '*)
  	   (<= object high))))
  
  (macrolet ((frob (num-type)
  	     `(define-presentation-method presentation-subtypep ((type
  								  ,num-type)
  								 maybe-supertype)
  	        (with-presentation-type-parameters (,num-type maybe-supertype)
  		  (let ((super-low low)
  			(super-high high))
  		    (with-presentation-type-parameters (,num-type type)
  		      (values (number-subtypep low high super-low super-high)
  			      t)))))))
    (frob real)
    (frob rational)
    (frob ratio)
    (frob float))
  
  (define-presentation-type character ())
  
  (define-presentation-method presentation-typep (object (type character))
  