do you have a link or reference to the paper or talk, please?
https://www.youtube.com/watch?v=EshxZVMURt4
https://popl18.sigplan.org/details/POPL-2018-papers/3/Formal...
The city is Los Angeles, though the content doesn't seem to match precisely what was mentioned.
I found this via a Google search for `conference convert legal phrases into code "theorem" bug`, which returned the following paper:
https://hal.inria.fr/hal-03159939v2/document
I then checked the citations of that paper for anything matching.
Oh wait, everyone was a nerdy person!