[1/2OT] B a finite set and the definition of "infinite set"

From: g (ig_at_g.g)
Date: 01/06/05 

Date: Thu, 06 Jan 2005 07:52:11 GMT

if f:B->B f[B]={y: exist x in B and f(x)=y}
Do you know why
Proposition
B is finite and f:B->B and (for all x, y that are in B and f(x)=f(y)
=> x=y)

then => f[B]=B
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What is your definition of "finite set" or "infinite set"?
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Proposition
B is finite /\ f:B->B /\ (Ax,y x,yeB/\f(x)=f(y) => x=y) => f[B]=B