The next letters on the list, if it comes to it, which it probably will, are epsilon, zeta, eta and theta. ALPHA, BETA, gamma, delta. The simplicity is obvious. The Greek alphabet was also used to label hurricanes last year after the traditional 21-name rotating list did not cover the amount of storms. The press in neutral Spain was not so constrained.
the greek alphabet used was limited to only one letter.
( z0 limit :ARG1 ( z1 alphabet :ARG1-of ( z2 use ) :mod ( z3 language :name ( z4 name :op "Greece" ) ) ) :ARG2 ( z5 letter :quant 1 :mod ( z6 only ) ) )
(z0 / limit-01
    :ARG1 (z1 / alphabet
              :ARG1-of (z2 / use-01)
              :mod (z3 / language
                       :name (z4 / name
                                 :op1 "Greece")))
    :ARG2 (z5 / letter
              :quant 1
              :mod (z6 / only)))
the greek alphabet used was limited to only one letter .
z3 :name z4
z4 :op1 1
z1 :mod z3
z1 :ARG1-of z2
z0 :ARG1 z1
z5 :quant 0
z5 :mod z6
z0 :ARG2 z5