Proof terms for infinitary rewriting, progress report
  We generalize the notion of proof term to the realm of transfinite reduction. Proof terms represent reductions in the first-order term format, thereby facilitating their formal analysis. We show that any transfinite reduction can be faithfully represented as an infinitary proof term, which is unique up to, infinitary, associativity.   Our main use of proof terms is in a definition of permutation equivalence for transfinite reductions, on the basis of permutation equations. This definition involves a variant of equational logic, adapted for dealing with infinite objects.   A proof of the compression property via proof terms is presented, which establishes permutation equivalence between the original and the compressed reductions. 
Carlos Lombardi, Alejandro R\'ios, Roel de Vrijer
cs.LO