Things Ai n't What They Used to Be is a 1942 jazz standard with music by Mercer Ellington and lyrics by Ted Persons.\n\nAnswer this question based on the passage: who wrote things ain't what they used to be
Use reasoning to answer the following question.
music by Mercer Ellington and lyrics by Ted Persons
To answer the above question, the relevant sentence is: "Things Ai n't What They Used to Be" is a 1942 jazz standard with music by Mercer Ellington and lyrics by Ted Persons.

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So, the final answer is music by Mercer Ellington and lyrics by Ted Persons