Exercise:

EXISTS x(I) FORALL y(I) [P(OI) y EQUIV P x] IMPLIES FORALL x P x OR FORALL x .~P x

You may not use ADVICE, but all other rules and commands 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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