  The production of K+ and K- mesons below and at the NN threshold is
summarized, based on a comparison of data with transport model calculations. K+
mesons are created in associate production together with hyperons (e.g. Lambda)
in multi-step processes involving Delta resonances. These processes occur
mainly during the high-density phase of the collision and this makes the K+ an
ideal tool to extract the stiffness of the nuclear equation of state, found to
be rather soft with a compressibility modulus K below 240 MeV. In contrast, the
major part of K- mesons are produced via strangeness exchange. Most of the
created K- are absorbed and the surviving ones are emitted quite late and at
low densities.

High Energy Physics - Phenomenology