  The algebraic structure of Thermo Field Dynamics lies in the $q$-deformation
of the algebra of creation and annihilation operators. Doubling of the degrees
of freedom, tilde-conjugation rules, and Bogoliubov transformation for bosons
and fermions are recognized as algebraic properties of $h_{q}(1)$ and of
$h_{q}(1|1)$, respectively.
