letter_class('L', "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"). letter_class('C', "bcdfghjklmnpqrstvwxyzBCDFGHJKLMNPQRSTVWXYZ"). letter_class('V', "aeiouAEIOU"). letter_class('N', "0123456789"). orthography_rewrite(" a V1", " an V1"). orthography_rewrite(" an C1", " a C1"). orthography_rewrite("_", " "). orthography_rewrite(" s ", "'s "). orthography_rewrite(" '", "'"). orthography_rewrite(" , ", ", "). orthography_rewrite("N1 : N2", "N1:N2"). orthography_rewrite("L1 : ", "L1: ").