```private val declarationItemsSection: Observable<List<PageOverviewSection>> = declarationsObservable
                    .map { listOfDeclaration ->
                        listOfDeclaration.groupBy {
                            it.date
                        }.toSortedMap(reverseOrder())
                    }
            .map {sorted ->

                val listOfNewItems = mutableListOf<PageOverviewItemsSection<*>>()

                sorted.values.flatten().forEachIndexed { index, declaration ->
                    val item = PageOverviewItemsSection(declaration)
                    if (sorted.keys.elementAtOrNull(index) != null) {
                        val subtitle = if (index == 0) { "EURO (€)" } else { "" }
                        item.sectionHeader = Pair(sorted.keys.elementAt(index), subtitle)
...

```/**
 * Returns a single list of all elements from all collections in the given collection.
 * @sample samples.collections.Iterables.Operations.flattenIterable
 */
public fun <T> Iterable<Iterable<T>>.flatten(): List<T> {
    val result = ArrayList<T>()
    for (element in this) {
        result.addAll(element)
    }
    return result
}