14 lines
288 B
Text
14 lines
288 B
Text
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import data.stream
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open nat
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namespace stream
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variable A : Type
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set_option pp.beta false
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theorem mem_of_mem_odd₂ (a : A) (s : stream A) : a ∈ odd s → a ∈ s :=
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assume ainos, obtain n (h : a = nth n (odd s)), from ainos,
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exists.intro (2*n+1) (by rewrite [h, nth_odd])
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end stream
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