Suppose f is a function such that f(f(x))=x for all x in the domain of f, and suppose that f(0)=2003. Find all roots of the equation f(x)=0
f( f(x) ) = x
So...
f( f(0) ) = 0 And f(0) = 2003 .
f( 2003 ) = 0
+647 
