Let $(Y, || ||)$ be a Banach space and $ l_y^\infty$ space of all bounded sequences by norm $ (y_n)\to sup\{ ||y_n|| : n∈N\}$. Prove that $L(l, Y) $ and $l_y^\infty $ are isometrically isomorphic spaces.
( where $L(l, Y)$ is space of all bounded linear operators $l\to Y$, and $l$ is space of all sequences in $Y$)
I don’t know how to constuct the isometric isomorphism.