[tz] [PROPOSED] New edition of Calendrical Calculations

[Paul Eggert]

* theory.html (Calendrical issues):
Update Reingold & Dershowitz citation to 4th edition.
---
 theory.html | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/theory.html b/theory.html
index 4d8726d..596b32c 100644
--- a/theory.html
+++ b/theory.html
@@ -1155,10 +1155,10 @@ based on guesswork and these guesses may be corrected or improved.
 Calendrical issues are a bit out of scope for a time zone database,
 but they indicate the sort of problems that we would run into if we
 extended the time zone database further into the past.
-An excellent resource in this area is Nachum Dershowitz and Edward M.
-Reingold, <cite><a
-href="https://www.cs.tau.ac.il/~nachum/calendar-book/third-edition/">Calendrical
-Calculations: Third Edition</a></cite>, Cambridge University Press (2008).
+An excellent resource in this area is Edward M. Reingold
+and Nachum Dershowitz, <cite><a
+href="https://www.cambridge.org/fr/academic/subjects/computer-science/computing-general-interest/calendrical-calculations-ultimate-edition-4th-edition">Calendrical
+Calculations: The Ultimate Edition</a></cite>, Cambridge University Press (2018).
 Other information and sources are given in the file '<code>calendars</code>'
 in the <code><abbr>tz</abbr></code> distribution.
 They sometimes disagree.
-- 
2.7.4