X5208 : %THEOREM%X5208 is a theorem.
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.
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