A Linux Command, a piece of human civilization

In the past, I was told that I could find a very strange month on Linux, but I forgot the special month. I searched online today and found that I learned a history of human civilization through this command (month. Haha. Although it has nothing to do with Linux, it is indeed because of Linux that I understand.

 

Daniel @ Daniel-LAPTOP :~ $ Cal 9 1752
September 17
October 6, 1234
1 2 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30

We found that September 2, 1752 was followed by 14, which is really strange. By searching online, we found the answer:

On May 25, February 1582, the Holy See requested to subtract 10 days from October 1582, so October 4, 1852 followed by 15 days. This is done in Italy, Spain, and other countries. The rest of the Catholic countries soon followed, but the new countries were reluctant to modify, and Orthodox countries such as Greece were not modified until the beginning of the 20th century, so the reform was in Britain and its colonies (including the United States) it was executed only on January 1, September 1752. In this way, September 2, 1752 is followed by September 14, 1752. This is why Cal generates the above output.

P.s.: Windows users are not lucky to find this special month, because Windows only covers 1980-2099. Haha ~~