[Israel.pm] Date manipulations

[Yona Shlomo]

Hello,

I have date items of the form yyyy-mm-dd and I'd like to be
able to manipulate them in the following ways:

Given such a date I'd like to ask ordinal questions such as:
what was the date k days before (e.g., what is the date
yesterday) or what will be the date n days from that date
(e.g., what's the date 10 days later).

What's a practical way to go about this?

Thanks.

-- 
Shlomo Yona
yona at cs.technion.ac.il
http://yeda.cs.technion.ac.il/~yona/