一直以为表示增量的Δ是个三角符号，今天发现Δ其实是希腊字母δ（Delta）的大写。

希腊字母表.png

另有希腊字母和罗马字母两个概念：
The Roman or Latin alphabet is the alphabet used to write many modern-day languages. It is the most used alphabet and writing system in the world today. It is the official script for nearly all the languages of Western Europe, and of some Eastern Europe languages. It is also used by some non-European languages such as Turkish, Vietnamese, Malay language, Swahili, and Tagalog. It is an alternative writing system for languages such as Hindi, Urdu, and Somali.The alphabet is a writing system which evolved from a western variety of the Greek alphabet.

The modern Greek alphabet has 24 letters.[1] It is used to write the Greek language.