@Override
	public int hashCode() {
		return Tree.hashCode(this);
	}
Return a sequence of all <em>mapped</em> nodes of the whole underlying
tree. This is a convenient method for
{@snippet lang="java":
final ISeq<B> seq = stream()
    .map(mapper)
    .collect(ISeq.toISeq());
}

@param mapper the mapper function
@param <B> the mapped type
@return a sequence of all <em>mapped</em> nodes
jenetics.ext/src/main/java/io/jenetics/ext/util/FlatTreeNode.java