the Laboratory frame can now
be obtained as follows \cite{AP}:
\begin{equation}
{\bf p} = \left(\frac {\p S}{\p {\bf r}}\right)_t = {\bf a}^\alpha k_\alpha +
m{\bf \dot u}
\ee          %33

\begin{equation}
H({\bf p,r},t) = -\left(\f{\p S}{\p t}\right)_{\bf r} = \eps + {\bf p \dot u} -
\frac{m{\dot u}^2}{2}
\ee         %34
where $\eps = \eps({\bf a}_\alpha({\bf p}-m{\bf \dot u}), g^{\alpha \beta})$ is
a periodic function of $\bf p$ with periods $2 \pi \hbar {\bf a}^\alpha$
determined by the reciprocal lattice vectors corresponding to the deformed
local lattice. This is the reason to call $\bf p$ {\it the quasimomentum of the
quasiparticle in $L$-system}.
\par
It follows from (33) that
\begin{equation}
k_\alpha = {\bf a}_\alpha ({\bf p}- m{\bf \dot u}) = {\bf ka}_\alpha.
\ee           %35
    Hence, the invariant quasimomentum components are equal to the scalar
product of the usual quasimomentum $\bf k$ in $C$-system and the primitive
vectors of the locally deformed lattice.
\par
The energy $\cal E$ of a quasiparticle in $L$-system obeys the Galilean law:
\begin{equation}
{\cal E} = \frac{m {\dot u}^2}{2} + m {\bf \dot u}\frac{\p \eps}{\p {\bf p}} +
\eps =  \frac{m {\dot u}^2}{2} + {\bf p}_0 {\bf \dot u} + \eps
\ee          %36
where $\dx {\bf p}_0= m 