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• Obags

Occs

Number of occurrences of a value in an obag.

Signature

(occs x bag) → occs

Arguments

bag — Guard (bagp bag).

Returns

occs — Type (natp occs).

Definitions and Theorems

Function: occs

(defun occs (x bag)
  (declare (xargs :guard (bagp bag)))
  (let ((__function__ 'occs))
    (declare (ignorable __function__))
    (cond ((emptyp bag) 0)
          ((equal x (head bag))
           (1+ (occs x (tail bag))))
          (t (occs x (tail bag))))))

Theorem: natp-of-occs

(defthm natp-of-occs
  (b* ((occs (occs x bag))) (natp occs))
  :rule-classes :rewrite)