  The embedding procedure of Batalin, Fradkin, and Tyutin, which allows to
convert a second-class system into first-class, is pushed beyond the formal
level. We explicitly construct, in all cases, the variables of the converted
first-class theory in terms of those of the corresponding second-class one.
Moreover, we only conclude about the equivalence between these two different
kind of theories after compairing their respective spectra of excitations.
