11 lines
266 B
Text
11 lines
266 B
Text
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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theorem mem_cons_of_mem₂ {a : A} {s : stream A} (b : A) : a ∈ s → a ∈ b :: s :=
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assume ains, obtain n h, from ains,
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exists.intro (succ n) begin rewrite [nth_succ, tail_cons, h] end
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end stream
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