POPLmark Challenge Via de Bruijn Indices

We present a solution to the POPLmark challenge designed by Aydemir et al., which has as a goal the formalization of the meta-theory of System F_<:. The formalization is carried out in the theorem prover Isabelle/HOL using an encoding based on de Bruijn indices. We start with a relatively simple formalization covering only the basic features of System F_<:, and explain how it can be extended to also cover records and more advanced binding constructs.