 Boltzmann Volterra operator

Combine the damped free-transport evolution and the linear Boltzmann collision operator in a time-ordered Bochner integral. Its norm obeys $\Vert \tau f(t){\Vert }_2\le C{\int }_0^t\Vert f(s){\Vert }_{2}ds$. This reduces the characteristic integral equation to $(I-\tau )f=U_a(t,0)f_0$.