[petemc_]

Nice, it even has the missing weeks in September 1752..

  $ wapm install zamfofex/greg@2020.10.10
  Package zamfofex/greg@2020.10.10 installed successfully!
  → Installed commands: greg
  $ cal 9 1752
     September 1752   
  Su Mo Tu We Th Fr Sa
         1  2 14 15 16
  17 18 19 20 21 22 23
  24 25 26 27 28 29 30

[zamfofex]

Well, I wanted to mention that to use the program, you should type ‘greg’, not ‘cal’. But it does also skip those couple days in 1752 with the same arguments: ‘greg 9 1752’.

[petemc_]

Whoops! Should have had my coffee before commenting. Cheers.

[EdSchouten]

I always find that behaviour somewhat arbitrary, as it was just the British empire that switched from the Julian to the Gregorian calendar that month. Most of mainland Europe already switched around 1582.