16 lines
552 B
Text
16 lines
552 B
Text
open scoped Classical
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/--
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error: Tactic `native_decide` failed. Error: failed to compile definition, consider marking it as 'noncomputable' because it depends on 'Classical.propDecidable', which is 'noncomputable'
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-/
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#guard_msgs in
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theorem ohno : False := by
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let f : Nat → Nat := fun n => if n=0 then 0 else
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if (∃ k, n = 2 * k) then n / 2 else 3 * n + 1;
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have h2 : f (f 2) ≠ 4 := by
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native_decide;
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have h2 : f (f 2) = 4 := by
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have : ∃ k, 2 = 2 * k := ⟨1, rfl⟩
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simp +decide +arith [f, this];
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omega
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contradiction
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