33 lines
754 B
Text
33 lines
754 B
Text
mutual
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def f : Nat → α → α → α
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| 0, a, b => a
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| n, a, b => g a n b |>.1
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def g : α → Nat → α → (α × α)
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| a, 0, b => (a, b)
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| a, n, b => (h a b n, a)
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def h : α → α → Nat → α
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| a, b, 0 => b
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| a, b, n+1 => f n a b
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end
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termination_by
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invImage
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(fun
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| Sum.inl ⟨_, n, _, _⟩ => (n, 2)
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| Sum.inr <| Sum.inl ⟨_, _, n, _⟩ => (n, 1)
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| Sum.inr <| Sum.inr ⟨_, _, _, n⟩ => (n, 0))
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(Prod.lex sizeOfWFRel sizeOfWFRel)
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decreasing_by
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simp [invImage, InvImage, Prod.lex, sizeOfWFRel, measure, Nat.lt_wfRel]
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first
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| apply Prod.Lex.left
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apply Nat.lt_succ_self
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| apply Prod.Lex.right
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decide
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#eval f 5 'a' 'b'
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#print f
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#print g
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#print h
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#print f._unary._mutual
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