Exercise:

EXISTS S(OI) FORALL x(I) [[S x OR P(OI) x] AND .~S x OR Q(OI) x] EQUIV FORALL y(I) .P y OR Q y

All rules and commands, including ADVICE, are allowed.

Only book theorems may be ASSERTed as lemmas without proof.

For a complete list of book theorems, type PROBLEMS.

No more help available. Sorry.

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