Solution
= Solution
{c}
\b[True.] For every $m,n$,
$$
\inf C_n\leq x_{m,n}\leq\sup R_m.
$$
Fix $m$. The number $\sup R_m$ is an <upper bound> for every column <infimum>, so $\sup_n\inf C_n\leq\sup R_m$. This holds for every $m$, making $\sup_n\inf C_n$ a <lower bound> of the row <suprema>. Taking their <infimum> gives the <weak minimax inequality>
$$
\boxed{\sup_{n\geq1}\inf_{m\geq1}x_{m,n}\leq\inf_{m\geq1}\sup_{n\geq1}x_{m,n}.}
$$