Given a type that is a Sequence of Sequences, how do I convert it to a single, flattened Sequence type? Consider the following Ceylon code:

```
Integer[] range(Integer max) {
    return [ for (idx in 1..max) idx ];
}

Integer[] prod(Integer max, Integer occurrences) {
    Integer[][] nestedSequence = [for (occurrence in 1..occurrences) range(max)];
    return // ??? something to produce a flattened sequence 
}

assert (prod(2, 2) == [1, 2, 1, 2]);

```

I'm experimenting with Ceylon for the first time and fumbling my way through the tutorials and API documentation. The [unzip method](http://modules.ceylon-lang.org/repo/1/ceylon/language/1.0.0/module-doc/index.html#unzip "unzip method") looks somewhat close to what I need, but not exactly.