The algebraic structure of thermo field dynamics lies in the q-deforma
tion of the algebra of creation and annihilation operators. Doubling o
f the degrees of freedom, tilde-conjugation rules, and Bogoliubov tran
sformation for bosons and fermions are recognized as algebraic propert
ies of h(q)(l) and of h(q)(l/l), respectively. (C) 1998 Elsevier Scien
ce B.V.