  Denote by $[0,\omega_1)$ the set of countable ordinals, equipped with the
order topology, let $L_0$ be the disjoint union of the compact ordinal
intervals $[0,\alpha]$ for $\alpha$ countable, and consider the Banach spaces
$C_0[0,\omega_1)$ and $C_0(L_0)$ consisting of all scalar-valued, continuous
functions which are defined on the locally compact Hausdorff spaces
$[0,\omega_1)$ and $L_0$, respectively, and which vanish eventually. Our main
result states that a bounded operator $T$ between any pair of these two Banach
spaces fixes a copy of $C_0(L_0)$ if and only if the identity operator on
$C_0(L_0)$ factors through $T$, if and only if the Szlenk index of $T$ is
uncountable. This implies that the set $\mathscr{S}_{C_0(L_0)}(C_0(L_0))$ of
$C_0(L_0)$-strictly singular operators on $C_0(L_0)$ is the unique maximal
ideal of the Banach algebra $\mathscr{B}(C_0(L_0))$ of all bounded operators on
$C_0(L_0)$, and that $\mathscr{S}_{C_0(L_0)}(C_0[0,\omega_1))$ is the
second-largest proper ideal of $\mathscr{B}(C_0[0,\omega_1))$. Moreover, it
follows that the Banach space $C_0(L_0)$ is primary and complementably
homogeneous.
