Solve a Debate

[John Machin]

On Feb 17, 9:57 am, castiro... at gmail.com wrote:
> > days_in_month = lambda m: m - 2 and 31 - ((m + 9) % 12 % 5 % 2) or 28
>
> > the guts of which is slightly more elegant than the ancient writing
> > from which it was derived:
>
> Lacks citation.

Maxima mea culpa.

Pages 294-295 (in particular formula 23.12) in "MAPPING TIME\nThe
Calendar and Its History", by E. G. Richards. OUP, 1998. ISBN
0-19-286205-7.