free-identifier=? on syntax-rules

free-identifier.scm

(import (scheme base) 
	(scheme write)
	(rename (only (scheme base) car) (car r5rs:car)))

(define-syntax free-identifier=??
  (syntax-rules ()
    ((_ a b)
     (let-syntax ((foo (syntax-rules (a)
			 ((_ a) #t)
			 ((_ _) #f))))
       (foo b)))))

(display (free-identifier=?? a a)) (newline)
(display (free-identifier=?? b a)) (newline)
(display (free-identifier=?? car r5rs:car)) (newline)