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数学家研究纯数学不是因为它有用;他研究它是因为他喜欢它,他喜欢它是因为它美丽。
The mathematician does not study pure mathematics because it is useful; he studies it because he delights in it and he delights in it because it is beautiful.
解释:看到兔子再回头唤猎狗,还不算太晚;跑掉了羊再去修补羊圈,也不算太迟。