“Mechanism Design for Acquisition of/Stochastic Evidence," with Elchanan Ben-Porath and Eddie Dekel, first preliminary draft September 2019, current draft August 2021.
“An Elementary Proof of the Optimality of Threshold Mechanisms," first draft June 2015, current draft July 2015.
This paper contains a much simpler proof of the main result in Ben-Porath, Dekel, and Lipman, "Optimal Allocation with Costly Verification." Yes, as Ricky Vohra says, the proof in the AER paper is a mess, but, unlike Ricky's proof, this very simple one doesn't assume finitely many IID types. (But I agree with Ricky about the reduced form... Ah, well, live and learn.)
“Why is Language Vague?," current draft, November 2009.
I still don't know, but I have some thoughts. I plan to update this paper sometime before 2030, give or take.