KotlinFlowCheckBlanks.kt

        val blank = { entry: Map.Entry<Int, LongWrapper> ->
            flowOf(max(0L, entry.value.get() - 
                       scrabbleAvailableLetters[entry.key - 'a'.toInt()]))
        }

        val nBlanks = { word: String ->
            flow {
                emit(histoOfLetters(word)
                    .flatMapConcat { map -> map.entries.iterator().asFlow() }
                    .flatMapConcat({ blank(it) })
                    .reduce { a, b -> a + b })
            }
        }

        val checkBlanks = { word: String ->
            nBlanks(word).flatMapConcat { l -> flowOf(l <= 2L) }
        }

        val score2 = { word: String ->
            flow {
                emit(histoOfLetters(word)
                    .flatMapConcat { map -> map.entries.iterator().asFlow() }
                    .flatMapConcat { letterScore(it) }
                    .reduce { a, b -> a + b })
            }
        }