Recognize a print specifier.
This is an ordinary std::defenum.
Function:
(defun print-specifier-p (x) (declare (xargs :guard t)) (or (eq x 'nil) (eq x ':error) (eq x ':result) (eq x ':info) (eq x ':all)))
Theorem: type-when-print-specifier-p
(defthm type-when-print-specifier-p (implies (print-specifier-p x) (if (if (symbolp x) (if (not (equal x 't)) (not (equal x 'nil)) 'nil) 'nil) 't (equal x 'nil))) :rule-classes :compound-recognizer)