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Least But Not The Last (Posted on 2003-05-08) Difficulty: 4 of 5
Prove that every Non-Empty set of Positive Integers contains a "Least Element".

See The Solution Submitted by Ravi Raja    
Rating: 2.7500 (8 votes)

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re: Proof by Contradiction Comment 13 of 13 |
(In reply to Proof by Contradiction by friedlinguini)

I came up with something similar:


Let S be a non-empty set of positive integers. Let I be a binary sequence indexing the integers in S, where bit i of I is 1 if and only if i is in S. For example, if S is {1, 3, 5}, then I is 10101000...

Since S is non-empty, I clearly has a first occurrence of 1 somewhere. That occurrence of 1 clearly corresponds to the least element of S.

  Posted by Caleb on 2019-04-02 23:23:02
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