(defun read-bit-vector (stream ch)
  (let* ((size (read stream))
         (bits (read stream))
         (vector (make-array size :element-type 'bit :initial-element 0)))
    (dolist (bit bits vector)
      (setf (aref vector bit) 1))))
(set-macro-character #\𝔟 'read-bit-vector)
(bit-and 𝔟10(1 2 3) 𝔟10(3 5 6))
--> #*0001000000