// Convert to an obligatory rewrite transducer
public static Fst ToRewriter(this Fst fst, ISet <char> alphabet)
{
var all = FsaBuilder.All(alphabet);
var notInDomain = all
.Difference(all.Concat(fst.Domain()).Concat(all))
.Identity()
.Optional();
return(notInDomain.Concat(fst.Concat(notInDomain).Star()));
}
// Convert an FST to an optional rewrite transducer
public static Fst ToOptionalRewriter(this Fst fst, ISet <char> alphabet)
{
var idAll = FsaBuilder.All(alphabet).Identity();
return(idAll.Concat(fst.Concat(idAll).Star()));
}