May 8th, 2015, 05:20 PM  #1 
Member Joined: Mar 2015 From: Brasil Posts: 90 Thanks: 4  Real Analysis.
Let $X$ be a set with $n$ elements. Use induction to prove that the set of bijections (permutations) $f:X\rightarrow X$ has $n!$ elements.

May 9th, 2015, 01:36 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,556 Thanks: 600 
Order the elements. First element has n possible images, second element has n1, etc.


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!real, analysis, real 
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