Solution
= Solution
The two transport equations are
$$
\partial_tp_+=-s\partial_xp_+-\lambda_+p_++\lambda_-p_-,
$$
$$
\partial_tp_-=s\partial_xp_-+\lambda_+p_+-\lambda_-p_-.
$$
For $p=p_++p_-$ and $j=s(p_+-p_-)$ they become
$$
p_t=-j_x,
\qquad
j_t=-s^2p_x+2sb c'(x)p-2\lambda_0j.
$$
Eliminating $j$ gives the closed <chemotactic telegraph equation>
$$
\boxed{p_{tt}+2\lambda_0p_t=s^2p_{xx}
-2sb\,\partial_x[c'(x)p].}
$$