- #1
Newtime
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Homework Statement
for n[tex]\in[/tex]N and [tex]\phi[/tex]: {1,...,n} [tex]\rightarrow[/tex] {1,...,n}. Prove [tex]\phi[/tex] is 1-1 if and only if it is onto.
The second part of this is to prove that if E is a finite set and f:E[tex]\rightarrow[/tex]E then f is 1-1 iff f is onto.
Homework Equations
There are several (many) theorems which could be usefl, but all of them are standard logical ones which don't really need to be restated, and I will cite all theorems used in my attempt at a solution below.
The Attempt at a Solution
I used induction but I have a strong suspicion I made a logical error so let me start by saying that in truth, I don't really know how to approach this problem because we are given so little. I can't say that {1,...,n} is a finite set so there has to be a 1-1 function from {1,...,n} onto it because I can't say that the set is "finite" simply by looking. Actually, I can say that, and it is finite, but in the proof, I certainly cannot simply say this. Also, proving both parts of thsi has been proving to be a challenge. Proving that 1-1 implies it is onto seems easier than proving the function is onto implies it is 1-1. I'm just sort of lost and frustrated. But here's my attempt in it's entirety:
(it's the attached image, I typed it up on MAPLE)
Also, I have a little scribbled out for proving that if the function is onto then it is 1-1 but I didn't get as far and any help there would be appreciated.
Thanks in advance for the help.
edit: also, for the second part of thsi problem, proving the same thing but for a generalized finite set, I think this would be substantially easier because I could reference the above proofs and also because I could use the definition of finite.