  Plastino and Curado [Phys. Rev. E 72, 047103 (2005)] recently determined the
equilibrium probability distribution for the canonical ensemble using only
phenomenological thermodynamical laws as an alternative to the entropy
maximization procedure of Jaynes. In the current paper we present another
alternative derivation of the canonical equilibrium probability distribution,
which is based on the definition of the Helmholtz free energy (and its being
constant at the equilibrium) and the assumption of the uniqueness of the
equilibrium probability distribution. Noting that this particular derivation is
applicable for all trace-form entropies, we also apply it to the Tsallis
entropy showing that the Tsallis entropy yields genuine inverse power laws.
