Common Lisp special variables in closure

I'm stumbling on a problem to capture special variables:

This works:

(let ((a 2))
  (declare (special a))
  (funcall
   (lambda (x)
     (declare (special a))
     (+ a (* x 3)))
   3))

=> 11

But this doesn't work:

(funcall
 (let ((a 2))
   (declare (special a))
   (lambda (x)
     (declare (special a))
     (funcall
      (lambda (x)
        (declare (special a))
        (+ a (* x 3)))
      x)))
 3)

=> The variable a is unbound.

It seems, a closure can't be used for dynamic scope. Is there a way to get it done without polluting the global namespace?

Answer

I found the following solution, which works in my use-case:

(funcall
 (lambda (x)
   (let ((a 2))
     (declare (special a))
     (funcall
      (lambda (x)
        (declare (special a))
        (+ a (* x 3)))
      x)))
 3)