Friday, September 8, 2017

elementary set theory - Bijection between mathbbN+timesmathbbR+ and mathbbR+



Let N+ denote the set of natural numbers bigger than 0 and let R+ denote the set of real numbers bigger than 0.




Is there a way to write down an explicit bijection between N+×R+ and R+?


Answer



You can replace N+ by N={0,1,2...}. Also ψ:R+[0,1).
Then the required bijection can be
N×R+(n,r)n+ψ(r)R+ .


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