Let fff and ggg be functions such that (f∘g)(x)=x(f \circ g)(x) = x(f∘g)(x)=x. Are fff and ggg inverses?
Yes, always
No, never
Yes, if (g∘f)(x)=x(g \circ f)(x) = x(g∘f)(x)=x also holds
Only if both are linear