プールの帰りに立ち読み。
英語で「~20」と書いたら、「約20」という意味があるということを初めて知った。"~ 20" は "≤ 20"と同じだと思っていた。論文を読むときには気を漬け菜毛ラバ。もとい、気をつけなければ。どうもタイピングの調子が悪い。
Wikipediaには、「20まで」と「約20」の両方について記述がある。
http://en.wikipedia.org/wiki/Tilde
（傍線は引用者）
Punctuation
It is sometimes used as punctuation (instead of a hyphen or dash) between two numbers, to indicate that they are a range, rather than subtraction, or a hyphenated number (such as a part number or model number). Japanese and other Asian languages almost always use this convention, but it is often done for clarity in other languages as well. For example: 12~15 means "12 to 15", ~3 means "up to three" and 100~ means "100 and greater". In Japanese, the tilde is also used to separate a title and a subtitle in the same line.
In the MMORPG community, the tilde is used as an ending punctuation of a sort. It usually indicates bemusement.
The tilde is also used in instant messaging and other online chat communities, to indicate sarcasm.
Mathematics
In mathematics, the tilde, often pronounced "twiddle," is often used to denote an equivalence relation between two objects. Thus x ~ y means x "is equivalent to" y.In English, it is often used to mean "approximately". Therefore, ~10 would be "about 10". Similar symbols are used in mathematics, such as in π ≈ 3.14, "π is about equal to 3.14". Since the double-tilde (≈) is not available from the keyboard, the tilde (~) became a substitute when typing. There is also a triple-tilde (≋), which is used to show congruence.
