Number (4): Everything in this space must add up to 4. The answer is 4-0, placed horizontally.
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，更多细节参见91视频
const writer = createBufferWriter();，详情可参考旺商聊官方下载
currentStep = currentStep.next(recordedEvent.result);
Under the new API design, transforms should not perform any work until the data is being consumed. This is a fundamental principle.