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| theory Scratch | |
| imports Main | |
| begin | |
| lemma | |
| shows "∀x. P x" | |
| proof - | |
| { | |
| fix t | |
| have "P t" sorry | |
| } | |
| thus "∀x. P x" .. (* valid deduction *) | |
| qed | |
| lemma | |
| shows "∀x. P x" | |
| proof - | |
| { | |
| have "P t" sorry | |
| } | |
| thus "∀x. P x" .. (* invalid deduction *) | |
| qed | |
| end |
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