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命题:\(\displaystyle\lim_{n\to\infty}\{m\in\mathbb{N}^+: m>n\}=\varnothing\).
证:易见 \(n>N=k-1\implies k< n+1\).
\(\quad\;\)故对任意\(k\in\mathbb{N}^+,\) 存在\(N=k-1\),对任意\(n>N\)
\(\quad\;\, k\not\in\{n+1,n+2,\ldots\}\)从而\(k\not\in\displaystyle\lim_{n\to\infty}\{n+1,n+2,\ldots\}\)
\(\therefore\;\displaystyle\lim_{n\to\infty}\{m\in\mathbb{N}^+:m>n\}=\varnothing.\quad\square\) |
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