[Avodah] R. Reisman's question

[Micha Berger]

In the spirit of the Gra, let me fill in one yad of secular knowledge
so that we can hopefully gain 100 yadayim of Torah.

In programming, there is the off-by-one error. If you want to build a
split-rail fence 100' long, with uprights every 10', how many uprights
will you need? The intuitive answer is (100 / 10 =) 10. However, this is
putting a fence-post 10' from the start, then 20', 30', etc... to 100'.
But you also need a post at the start itself -- 11 fence-posts in all.

We face a parallel problem routinely when you want to do something to
items numbered m through n in an array (or vector or list). You would
think that means looping over n - m items, but really it's n - m + 1!

E.g. Say you want to visit items 3, 4 and 5. That's three items, but
5 - 3 is only 2. (Really you want 5 - 2, as 2 is the highest numbered
item not visited.)

This creates a gap between cardinal and ordinal numbers, when counting
lengths or durations (measuring, rather than outright counting). The 8th
day does refer to an 8 day set -- when the child is 0, 1, 2, 3, 4, 5, 6,
and 7 days old respectively. So the child is only 7 days old. The first
day the child is 0 days old. Much like the neglected fence-post at the
starting point.

Second issue:

In measuring people's ages, we appear to use the days as a unit. We
don't worry about whether the person was born shortly after tzeis or
shortly before the following sheqiah.

So, he's 13 + yom echad the moment he entered the yom echad of his
birthday. (Miqtzas hayom kekulo?)

Tir'u baTov!
-Micha

-- 
Micha Berger             I thank God for my handicaps, for, through them,
micha at aishdas.org        I have found myself, my work, and my God.
http://www.aishdas.org                - Helen Keller
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