Comment by chalst

Tromp's binary lambda calculus, which is what Justine is using, is based on de Bruijn indices.

It works, but it's very fiddly. My favourite way of solving the problem of names in the lambda calculus is to use Pitts-Gabbay nominal syntax. Wikipedia has a weak article on them, which I mean someday to fix up: https://en.wikipedia.org/wiki/Nominal_terms_(computer_scienc...