微積分 6.3

無限年 3.3

這段改編自 2010 年 4 月 3 日的對話。

這個定義,填補了「微積分」原本的漏洞。

(安:「微積分」原本有什麼漏洞?)

原本的漏洞,在於使用了「無限小」這個字眼,而又沒有明確講述,「無限小」究竟是什麼意思。

This work is in the public domain in the United States, and those countries with a copyright term of life of the author plus 100 years or less.
This work is in the public domain in the United States, and those countries with a copyright term of life of the author plus 100 years or less.

「微積分」的發明者,和早期的使用者,都對「無限小」的意思含糊其詞,例如:

「無限小」小過任何其他數,但它本身又不是零。(簡化起見,這裡不討論負數。)

這個講法的問題,在於自相矛盾:

即使 x = 無限小,x/2(x 的一半)理應仍然會小於 x 本身。但是,你又宣稱,x 會小於任何其他數。結論是,x 既會小於 x/2,又會大於 x/2,自相矛盾也。

— Me@2013.03.04

2013.03.04 Monday (c) All rights reserved by ACHK

Emacs, 2

Nice to see Emacs getting a bit of press recently. I’ve used it for almost 20 years now and it dominates my time at the keyboard. It isn’t perfect and I’m reluctant to recommend it but I wouldn’t want to be without it. Let me explain.

The best thing about Emacs is that it can do everything (including the things it can’t do yet). The worst thing about Emacs is finding out how it does anything. I wouldn’t call it discoverable. In fact, on several occasions, I’ve learned about Emacs by accident: you press the wrong key combination (easy to do when you’re holding down a couple of keys and stretching for a third) and, look, something interesting happens!

— Accidental Emacs

— 2008-05-06 

— Thomas Guest

2013.03.04 Monday ACHK

Overprolific Alpha Geeks

Everyone, including Alpha Geeks, use only one app:

People complain about how their work wants them to use organizers…

Joel Splosky uses Excel for everything.

HR person sends website designs in PPT.

Don Lancaster sees the world in Postscript.

— Running notes from

Life Hacks: Tech Secrets of Overprolific Alpha Geeks

— Danny O’Brien

— 11 February, 2004

— by Cory Doctorow

2013.03.03 Sunday ACHK