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Pick-a-point-subset-strategy

Automatic pick-a-point proofs of subset.

The rewrite rule pick-a-point-subset-strategy tries to automatically reduce proof goals such as:

(implies hyps
         (subset X Y))

To proofs of:

(implies (and hyps (in a X))
         (in a Y))

The mechanism for doing this is somewhat elaborate: the rewrite rule replaces the (subset X Y) with (subset-trigger X Y). This trigger is recognized by a computed hint, which then suggests proving the theorem via functional instantiation of all-by-membership.

The pick-a-point method is often a good way to prove subset relations. On the other hand, this rule is very heavy-handed, and you may need to disable it if you do not want to use the pick-a-point method to solve your goal.

Definitions and Theorems

Function: subset-trigger

(defun subset-trigger (x y)
  (declare (xargs :guard (and (setp x) (setp y))))
  (subset x y))

Theorem: pick-a-point-subset-strategy

(defthm pick-a-point-subset-strategy
 (implies
  (and
      (syntaxp (rewriting-goal-lit mfc state))
      (syntaxp
           (rewriting-conc-lit (cons 'subset (cons x (cons y 'nil)))
                               mfc state)))
  (equal (subset x y)
         (subset-trigger x y))))

Function: pick-a-point-subset-hint

(defun pick-a-point-subset-hint
       (id clause world computed-hints::stable)
 (declare (ignore id world))
 (if (not computed-hints::stable)
     nil
  (let
   ((computed-hints::triggers
         (computed-hints::harvest-trigger clause 'subset-trigger)))
   (if (not computed-hints::triggers)
       nil
    (let*
     ((computed-hints::others
           (set-difference-equal clause computed-hints::triggers))
      (computed-hints::hyps
           (computed-hints::others-to-hyps computed-hints::others))
      (computed-hints::fi-hints
           (computed-hints::build-hints
                computed-hints::triggers
                'all-by-membership
                'all-hyps
                'all-set
                'predicate
                'all
                'subset
                computed-hints::hyps
                '(((predicate ?x ?y) (in ?x ?y)))))
      (computed-hints::hints
           (list :use computed-hints::fi-hints
                 :expand computed-hints::triggers)))
     (prog2$
      (cw
       "~|~%Attempting to discharge subgoal by a ~
                            pick-a-point strategy; disable ~x0 to ~
                            prevent this.~%~%"
       'pick-a-point-subset-strategy)
      computed-hints::hints))))))

Theorem: pick-a-point-subset-constraint-helper

(defthm pick-a-point-subset-constraint-helper
  (implies (syntaxp (equal set-for-all-reduction
                           'set-for-all-reduction))
           (equal (subset set-for-all-reduction rhs)
                  (cond ((emptyp set-for-all-reduction) t)
                        ((in (head set-for-all-reduction) rhs)
                         (subset (tail set-for-all-reduction)
                                 rhs))
                        (t nil)))))