  It is argued that an irregularity in the baryon stopping is a natural
consequence of a phase transition occurring in the compression stage of a
nuclear collision. It is a combined effect of the softest point inherent in an
equation of state (EoS) with a phase transition and a change in the
nonequilibrium dynamics from hadronic to partonic transport. Thus, this
irregularity is a signal from a hot and dense stage of the nuclear collision.
In order to illustrate this proposition, calculations within the three-fluid
model were performed with three different EoS's: a purely hadronic EoS, an EoS
with a first-order phase transition and that with a smooth crossover
transition. It is found that predictions within the first-order-transition
scenario indeed reveal an a strong irregularity in the incident energy
dependence of the form of the net-proton rapidity distributions in central
collisions. This behavior is in contrast to that for the hadronic scenario,
where the distribution form gradually evolve, displaying no irregularity. The
case of the crossover EoS is intermediate. Only a weak irregularity takes
place. Experimental data also exhibit a trend of similar irregularity, which is
however based on still preliminary data at energies of 20A GeV and 30A GeV.
