class MainActivityViewModel(//...) :
    ViewModel() {
    //...
    val words: MediatorLiveData<PagedList<Meaning>> = MediatorLiveData()
    //...

    private fun addAllWordsAndRemoveSearch() {
        removeSearchObserver()
        if (!mapOfLiveData.containsKey(ALL)) {
            mapOfLiveData[ALL] = LivePagedListBuilder(dataSourceFactory, config).build()
            words.addSource(mapOfLiveData[ALL]!!) {
                words.value = it
            }
        }
    }

    private fun addSearchAndRemoveAllWords() {
        removeAllWordsObserver()
        if (!mapOfLiveData.containsKey(SEARCH)) {
            mapOfLiveData[SEARCH] = LivePagedListBuilder(searchDataSourceFactory, config).build()
            words.addSource(mapOfLiveData[SEARCH]!!) {
                words.value = it
            }
        }
    }
    //...
}