  This paper is an electronic application to my set of lectures,
subject:`Formal methods in solving differential equations and constructing
models of physical phenomena'. Addressed, mainly: postgraduates and related
readers.
  Content: a very detailed discussion of the simple model of interaction based
on the equation array: d^2 q(t)/dt^2 =-\Omega^2(q(t)-Q(t))+f_0(t),
d^2u(t,x)/t^2=c^{2}d^2 u(t,x)/dx ^2 -4\gamma c\delta(x-x_0)(Q(t)-q(t))
+f_1(t,x), Q(t) = u(t,x_0) . Besides, less detailed discussion of related
models. Central mathematical points: d'Alembert-Kirchhoff-like formulae.
Central physical points: phenomena of Radiation Reaction, Braking Radiation and
Resonance.
