Flash fill is an implementation of program synthesis, a technique invented by Sumit Gulwani formerly of Microsoft Research. Here's a paper that explains more about how it works [1]. It's not a very discoverable feature of Excel though [2]

[1] https://arxiv.org/pdf/1703.03539.pdf [2] https://support.microsoft.com/en-us/office/using-flash-fill-...

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