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