Which property defines a function fff that is an involution?
f(f(x))=xf(f(x)) = xf(f(x))=x
f−1(x)=f(x)f^{-1}(x) = f(x)f−1(x)=f(x)
f(x)=f−1(x)f(x) = f^{-1}(x)f(x)=f−1(x)
All of the above