@Override public Xform<A> concat(Iterable<? extends A> list) {
        if (list == null) { throw new IllegalArgumentException("Can't concat a null iterable"); }
        return new AppendIterDesc<>(this, new SourceProviderIterableDesc<>(list));
    }
@ Override public Xform < A > concat ( Iterable < ? extends A > list ) { if ( list == null ) { throw new IllegalArgumentException ( "Can't concat a null iterable" ) ; } return new AppendIterDesc < > ( this , new SourceProviderIterableDesc < > ( list ) ) ; }
}