This Excel lambda function returns TRUE for a leap year and FALSE for all other years

excel-lambda-ISLEAPYEAR.txt

/*
ISLEAPYEAR

Calculates whether a year is a leap year

Inputs:
  - yr is the year you want to test
  
Returns:
  TRUE if the year is a leap year, FALSE otherwise
  
Notes:
  Per the documentation, Excel includes a bug that treats 1900 as a leap year.
  https://docs.microsoft.com/en-us/office/troubleshoot/excel/wrongly-assumes-1900-is-leap-year


*/

ISLEAPYEAR =LAMBDA(yr,
  (
   (yr<>1900)
  *(MONTH(DATE(yr,2,29))=2)
  )=1
);