  We reexamine in the relativistic transport model the dependence of kaon yield
on the nuclear equation of state in heavy ion collisions at energies that are
below the threshold for kaon production from the nucleon-nucleon interaction in
free space. For Au+Au collisions at 1 GeV/nucleon, we find that the kaon yield
measured by the Kaos collaboration at GSI can be accounted for if a soft
nuclear equation of state is used. We also confirm the results obtained in the
non-relativistic transport model that the dependence of kaon yield on the
nuclear equation of state is more appreciable in heavy ion collisions at lower
incident energies. We further clarify the difference between the predictions
from the relativistic transport model and the non-relativistic transport model
with a momentum-dependent potential.
