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Re:Sentinel Value by zapf on Saturday January 25, 2020 @04:56AM (#22145626) 

       1. Go to Africa.
       2. Put an elephant in Cairo.
       3. Start at the Cape of Good Hope.
       4. Work northward in an orderly manner, traversing the continent alternately east and west,
       5. During each traverse pass:

               1. Catch each animal seen.
               2. Compare each animal caught to a known elephant.
               3. Stop when a match is detected.

        6. If you are in Cairo, then there are no elephants in Africa (other than the one you placed there).
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Re:Sentinel Value by dragonwriter on Saturday January 25, 2020 @05:08AM (#22145658)
This approach doesn't work.

The sentinel elephant you place has to be closer to Algiers than Cairo, or you risk false negatives.

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Re:Sentinel Value by zapf on Saturday January 25, 2020 @04:53AM (#22145617)
TIL: A sentinel value is sometimes known as an "Elephant in Cairo", due to a joke where this is used as a physical sentinel.

https://en.wikipedia.org/wiki/Elephant_in_Cairo

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