Let g○f be bijective on sets a to a.

Suppose that g is not surjective, then R(g○f)? R(g)？ A, that is, R(g○f)? A, so g○f can't be surjective, so it can't be bijective, which contradicts the meaning of the question, so the assumption is not true and G is surjective.

Suppose f is not an event, then? A, b∈A, a≠b, where f(a)=f(b)

Then (G○F) (a) = g (f (a)) = g (f (b)) = (G○F) (b), that is, G ○ f is not an accident, so G ○ f can't be a bijection, which contradicts the meaning of the question, so the assumption is not true and F is an accident.