Which of the two statements do you find is easier to understand?

WHERE (txv.business_unit2tcode NOT IN (41940)

        OR (txv.business_unit2tcode IN (41940) AND txv.ext_source_key IS NULL)); *OR*

WHERE CASE           WHEN txv.business_unit2tcode = 41940

          THEN              CASE

                WHEN txv.ext_source_key IS NULL THEN 'true'

                ELSE 'false'

             END

          ELSE

             'true'

       END = 'true';

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