DISJUNCTS_ACDrule.DISJUNCTS_AC : term * term -> thmProve equivalence under idempotence, symmetry and associativity of disjunction.
DISJUNCTS_AC takes a pair of terms (t1, t2)
and proves |- t1 = t2 if t1 and
t2 are equivalent up to idempotence, symmetry and
associativity of disjunction. That is, if t1 and
t2 are two (different) arbitrarily-nested disjunctions of
the same set of terms, then DISJUNCTS_AC (t1,t2) returns
|- t1 = t2. Otherwise, it fails.
Fails if t1 and t2 are not equivalent, as
described above.
- DISJUNCTS_AC (Term `(P \/ Q) \/ R`, Term `R \/ (Q \/ R) \/ P`);
> val it = |- (P \/ Q) \/ R = R \/ (Q \/ R) \/ P : thmUsed to reorder a disjunction. First sort the disjuncts in a term
t1 into the desired order (e.g., lexicographic order, for
normalization) to get a new term t2, then call
DISJUNCTS_AC(t1,t2).