lean2/tests/lean/run/rewrite_with_beta.lean

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import data.stream
open nat
namespace stream
variable A : Type
theorem mem_cons_of_mem₂ {a : A} {s : stream A} (b : A) : a ∈ s → a ∈ b :: s :=
assume ains, obtain n h, from ains,
exists.intro (succ n) begin rewrite [nth_succ, tail_cons, h] end
end stream