"Things Ai n't What They Used to Be" is a 1942 jazz standard with music by Mercer Ellington and lyrics by Ted Persons.

Answer this question based on the passage: who wrote things ain't what they used to be? OK. Let's think. My stream of consciousness:
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. The answer is music by Mercer Ellington and lyrics by Ted Persons.