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37 lines
453 B
Plaintext
37 lines
453 B
Plaintext
2 years ago
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import NNG.Metadata
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import NNG.MyNat.Addition
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import Std.Tactic.RCases
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Game "NNG"
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World "AdvProposition"
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Level 10
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Title ""
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open MyNat
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Introduction
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"
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"
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Statement
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""
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(P Q : Prop) : (¬ Q → ¬ P) → (P → Q) := by
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by_cases p : P
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· by_cases q : Q
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intro h p' -- cc
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assumption
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intro h p'
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have g : ¬ P := h q
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contradiction
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· by_cases q : Q
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intro h p
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assumption
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intro h p
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contradiction
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Conclusion
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"
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"
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