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Insert-underscores

Definitions and Theorems

Function: insert-underscores

(defun insert-underscores (x)
  (declare (xargs :guard t))
  (cond ((atom x) x)
        ((equal (mod (len x) 4) 0)
         (list* #\_ (car x)
                (insert-underscores (cdr x))))
        (t (list* (car x)
                  (insert-underscores (cdr x))))))

Theorem: character-listp-of-insert-underscores

(defthm character-listp-of-insert-underscores
  (implies (force (character-listp x))
           (character-listp (insert-underscores x))))