Is this the same Luhn that brought us the Luhn checksum for checking the validity of credit card numbers?

Yes.

Stop words are also attributed to him. https://en.wikipedia.org/wiki/Stop_word#History_of_stop_word...

Also KWIC indices, hashing, ...[1]

[1] https://en.wikipedia.org/wiki/Hans_Peter_Luhn

Yes, the same Hans Peter Luhn (German-born U.S.-American researcher mostly with IBM R&D - https://en.wikipedia.org/wiki/Hans_Peter_Luhn). He also single-handedly invented automatic document summarization and knowledge management.

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