Title: Locally Nameless Permutation Types,
Abstract: We define "Locally Nameless Permutation Types", which fuse permutation types
as used in Nominal Isabelle with the locally nameless representation. We show
that this combination is particularly useful when formalizing programming
languages where bound names may become free during execution ("extrusion"),
common in process calculi. It inherits the generic definition of permutations
and support, and associated lemmas, from the Nominal approach, and the ability
to stay close to pencil-and-paper proofs from the locally nameless approach. We
explain how to use cofinite quantification in this setting, show why reasoning
about renaming is more important here than in languages without extrusion, and
provide results about infinite support, necessary when reasoning about
countable choice.