Suppose that X is contained in Y, and Y is contained in Z,
where X, Y, and Z all are metric spaces. Show that X is compact
relative to Y iff X is compact relative to Z.
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█▆█ █ ▊█ ◢██ ▊▊█ █▆█ └╯└〒▽〒└╯└◥ ◤
█ ██ ██ ◥▆▆ ███ ◢◤█ 摸狗狗退散 ▇▅▄▆
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