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Oct-escape

Oct-escapep

Recognizer for oct-escape structures.

Signature
(oct-escapep x) → *

Definitions and Theorems

Function: oct-escapep

(defun oct-escapep (x)
  (declare (xargs :guard t))
  (and (consp x)
       (cond ((or (atom x) (eq (car x) :one))
              (and (b* ((digit (cdr x)))
                     (oct-digit-char-p digit))))
             ((eq (car x) :two)
              (and (consp (cdr x))
                   (b* ((digit1 (car (cdr x)))
                        (digit2 (cdr (cdr x))))
                     (and (oct-digit-char-p digit1)
                          (oct-digit-char-p digit2)))))
             (t (and (eq (car x) :three)
                     (and (consp (cdr x))
                          (consp (cdr (cdr x))))
                     (b* ((digit1 (car (cdr x)))
                          (digit2 (car (cdr (cdr x))))
                          (digit3 (cdr (cdr (cdr x)))))
                       (and (oct-digit-char-p digit1)
                            (oct-digit-char-p digit2)
                            (oct-digit-char-p digit3))))))))

Theorem: consp-when-oct-escapep

(defthm consp-when-oct-escapep
  (implies (oct-escapep x) (consp x))
  :rule-classes :compound-recognizer)