  A detailed study of pion production in central Mg-Mg collisions at a momentum
of 4.3 GeV/c per incident nucleon was carried out with use of the setup GIBS.
The average kinematical characteristics of pions (multiplicity n_, momentum P,
transverse momentum P_{T}, emission angle Q, rapidity Y) and corresponding
distributions have been obtained. The experimental results have been compared
with the predictions of the Quark Gluon String Model (QGSM) and satisfactory
agreement between the experimental data and the model has been found. The QGSM
reproduces also the dependence of average P_{T} on n_{-}.
  The temperatures of pi^{-} mesons have been estimated in the rapidity
interval of 0.5<=Y<=2.1. A satisfactory fit for pi^{-} mesons has been achieved
by using a form involving two temperatures T_{1} and T_{2}. It was found that
the QGSM underestimates T_{2} by (10-15)%.
  The data have been analyzed using the transverse momentum technique. The
observed dependence of the <P_{x'}(Y)> on Y shows the S-shape behaviour. The
slope at midrapidity F had been determined. The QGSM reproduces the <P_{x}>
distribution satisfactorily, but underestimates the parameter F.
