default Seq<Tuple2<T, T>> crossSelfJoin() {
        SeqBuffer<T> buffer = SeqBuffer.of(this);
        return crossJoin(buffer.seq(), buffer.seq());
    }
Cross join stream with itself into one.
<p>
<pre><code>
// (tuple(1, 1), tuple(1, 2), tuple(2, 1), tuple(2, 2))
Seq.of(1, 2).crossSelfJoin()
</code></pre>
jOOL/src/main/java/org/jooq/lambda/Seq.java