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Ascii-char-p

Recognize ASCII characters.

Function: ascii-char-p

(defun ascii-char-p (x)
  (declare (xargs :guard t))
  (and (characterp x)
       (< (char-code x) 128)))

Theorem: booleanp-of-ascii-char-p

(defthm booleanp-of-ascii-char-p
  (booleanp (ascii-char-p x))
  :rule-classes :type-prescription)

Theorem: characterp-when-ascii-char-p

(defthm characterp-when-ascii-char-p
  (implies (ascii-char-p x)
           (characterp x))
  :rule-classes :compound-recognizer)

Ascii-charlist-p: (ascii-charlist-p x) recognizes lists where every element satisfies ascii-char-p.
Ascii-chars: A character set for ascii-char-p.