$L^4$-norm of a random variable. Why is it computed like that?

51 Views Asked by At

Let's consider a random variable $\Delta(t)$ and consider that one has to compute:
$$||\sup\limits_{t\in[0,1]}|\Delta(t)|||_{L^4}$$ It is computed like:

$$||\sup\limits_{t\in[0,1]}|\Delta(t)|||_{L^4}=\mathbb{E}(\sup\limits_{t\in[0,1]}|\Delta(t)|^4)^{\frac{1}{4}}\tag{1}$$

However, shouldn't it be like:

$$||\sup\limits_{t\in[0,1]}|\Delta(t)|||_{L^4}=\mathbb{E}(\color{red}{(}\sup\limits_{t\in[0,1]}|\Delta(t)|\color{red}{)}^4)^{\frac{1}{4}}\tag{2}$$

?

Could I consider $(1)$ the same as $(2)$? If so, why?