Show that B can't be a proper subset of A

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SUMMARY

The discussion centers on proving that if there exists a one-to-one function f from set A onto set B, where B is a subset of A, then B cannot be a proper subset of A, implying B must equal A. The example provided illustrates this concept using integers and even integers, where the function f(n) = 2n is both onto and one-to-one, yet B (the even integers) does not equal A (the integers). This establishes that under these conditions, B must equal A rather than being a proper subset.

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Homework Statement


Let f be a function on A onto B where B is a subset of A, and f is a one-to-one function.
Now, I want to show that B can't be a proper subset of A( that is, not B[itex]\subset[/itex]A. this means B=A).


Homework Equations





The Attempt at a Solution


I attempted to solve this problem. Even though it is not complicated problem, but I don't have an idea how to prove it.

Could you give me a clue or something??
 
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gotjrgkr said:
Let f be a function on A onto B where B is a subset of A, and f is a one-to-one function.
Now, I want to show that B can't be a proper subset of A

hi gotjrgkr! :smile:

if A is the integers and B is the even integers, and if f:A -> B is defined by f(n) = 2n,

then f is onto and one-one, but B ≠ A :redface:
 


Thank you!
 

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