In 1964 Levin was hired to write a treatment (and potential screenplay) for a Universal Studios property titled "Mixed Doubles."
We've been unable to find any further info on what this project was, was based on, or became – if indeed anything further came of it. We'd welcome any info from parties with knowledge of the matter.
Given both the frothy title, and the fact that the matter arose a year after the release of the film adaptation of Levin's Critic's Choice, we suspect it was to be an urbane romantic comedy of some sort. ("Bob and Carol and Ted and Alice Play Tennis"?)