# Concept derivation guides

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Concept guide



## [A universal code for three natural-number tracks](/en/derivations/derivation-mko-at-most-countable-set-01/?from=%2Fen%2Fderivations%2F%3Fq%3Dmko-at-most-countable-set)

N0 times {0,1,2} injects into N0 by c(n,j)=3n+j and is at most countable.

At-most-countable set

derivation-mko-at-most-countable-set-01





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