(*
 * Determine if a letter is a vowel.
 *
 * E.g.
 *      A : Vowel -> t
 *      u : Vowel -> t
 *      R : Vowel -> f
 *
 * This function is used by function PigLatin.
 *)

DEF Vowel AS 
   [#<a e i o u A E I O U>, id] | member;
