  Classical XY spins on a two dimensional triangular lattice with
antiferromagnetic interactions are reconsidered. We find that the
Kosterlitz-Thouless transition associated to the U(1) symmetry appears at a
temperature 0.0020(2) below the Ising transition at 0.5122(1) associated to the
Z_2 symmetry. The Ising transition has critical exponents different from the
standard ones. Using extensive Monte Carlo simulations for equilibrium and
dynamical properties we show that the lack of universality observed in previous
studies is due to finite size corrections not taken account. Likewise the
Kosterlitz-Thouless transition has a critical exponent \eta\approx0.36 larger
than the corresponding standard value 0.25. Also the helicity jump at the
critical temperature is smaller than in the ferromagnetic case in disagreement
with theoretical predictions. We try using the concept of an "quasi
Universality class" to reconcile the standard critical behavior observable at
higher temperatures with the different quasi universal one close to the
critical region.
