ComplexAsyncfFowCleaner.kt

private fun prefetchData(): Completable =
    inParallel(
        async1() andThen async2() andThen (async3() alongside async4()),
        async1() andThen async5(),
        async6() andThen async7())

fun inParallel(vararg sources: CompletableSource): Completable = Completable.mergeArray(*sources)

infix fun Completable.andThen(next: CompletableSource): Completable = this.andThen(next)

infix fun Completable.alongside(other: CompletableSource): Completable = this.mergeWith(other)

fun async1(): Completable { TODO("not implemented") }
fun async2(): Completable { TODO("not implemented") }
fun async3(): Completable { TODO("not implemented") }
fun async4(): Completable { TODO("not implemented") }
fun async5(): Completable { TODO("not implemented") }
fun async6(): Completable { TODO("not implemented") }
fun async7(): Completable { TODO("not implemented") }

ComplexAsyncFlow.kt

private fun prefetchData(): Completable =
    Completable.mergeArray(
        async1().concatWith(async2()).concatWith(async3().mergeWith(async4())),
        async1().concatWith(async5()),
        async6().concatWith(async7()))

fun async1(): Completable { TODO("not implemented") }
fun async2(): Completable { TODO("not implemented") }
fun async3(): Completable { TODO("not implemented") }
fun async4(): Completable { TODO("not implemented") }
fun async5(): Completable { TODO("not implemented") }
fun async6(): Completable { TODO("not implemented") }
fun async7(): Completable { TODO("not implemented") }