@Override
	public ISeq<FlatTreeNode<V>> flattenedNodes() {
		return stream().collect(ISeq.toISeq());
	}
Return the index of the first child node in the underlying node array.
{@code -1} is returned if {@code this} node is a leaf.

@return Return the index of the first child node in the underlying node
        array, or {@code -1} if {@code this} node is a leaf
jenetics.ext/src/main/java/io/jenetics/ext/util/FlatTreeNode.java