a problem on composition of functions
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Let $f colon A to A$ be a function such that $f circ f=f$ . If $f$ is one-to-one then prove that $f$ is also onto. I know in my head that the func. $f$ is $f(x)=x$ , but I can't develop a proof for the above statement.
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edited 35 mins ago
user649511
asked 5 hours ago
user649511 user649511
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