  We consider a dynamical system on a metric graph, that corresponds to a
semiclassical solution of a time-dependent Schr\"odinger equation. We omit all
details concerning mathematical physics and work with a purely discrete
problem. We find a weak inequality representation for the number of points
coming out of the vertex of an arbitrary tree graph. We apply this construction
to an "H-junction" graph. We calculate the difference between numbers of moving
points corresponding to the permutation of edges. Then we find a symmetrical
difference of the number of points moving along the edges of a metric graph.
