Closed-graph proof for a factored operator
= Closed-graph proof for a factored operator
If bounded $S:X\to Y$ is injective and $\operatorname{im}T\subseteq\operatorname{im}S$, then $R=S^{-1}T$ has closed graph: $x_n\to x$ and $Rx_n\to z$ imply $Sz=Tx=S(Rx)$ and hence $z=Rx$.