Solution (source code)

= Solution

Reading the coefficients in the ordered concentration <vector> gives the <linear system of ordinary differential equations>
$$
\boxed{\dot x=Mx,\qquad M=\begin{pmatrix}-\epsilon&0&\delta\\\epsilon&-\eta&0\\0&\eta&-\delta\end{pmatrix}.}
$$
Its columns sum to zero, so $d(A+B+C)/dt=0$. This <three-state cyclic conversion model> conserves total concentration.