The capital of D is D, which is the fourth letter in Latin letters and English letters, and has different meanings in the International Phonetic Alphabet and Chinese Pinyin. After the title of the paper reference, it indicates the paper; The letter D is also used in physics, chemistry, music, names, etc.
D (capital); D (lowercase) is the fourth letter in Latin letters and English letters, which is different from Russian letters. д comes from the Greek letter δ.
"D" may be the symbol of a door, just like ancient Egyptian hieroglyphics. We can't know when it first appeared in Sumerian characters.
About 1000 BC, this symbol was a specific linear form in Biblus (the ancient Mediterranean port city of Jubail, located in the north of Beirut, Lebanon, and became a prosperous Phoenician city in the second millennium), other parts of Phoenicia and the center of Canaan. In semitic, it is called th, which means door.
The Greeks changed the name of Semu to Delta, and they kept the Phoenician symbol. In the Italian colony of Calchi (or Calchi-Calchi), the mother was slightly bent. This shape makes it also exist in Latin characters. Since the Latin era, this triangle has been gradually smoothed out.