bug in cal (1) - actually feature

[David Phillip Oster]

Cal is documented to behave this way. Read your man page!  By the way,
it is an interesting question what cal should do if you ask for a year
before 1752. Different calendars were adopted in different places at
different times. I have a few references about the early calendar see:

Knuth, Art of Computer Programming, Vol 1., p .155
See CACM, 5 (1962) p. 209 - 210 for Easter < 1582
see also, Puzzles and Paradoxes, T. H. O'Beirne 
London:Oxford U. Press, 1965, Chap. 10

Anybody have any good references for early calendars?