Proving Soundness of Extensional Normal-Form Bisimilarities
Normal-form bisimilarity is a simple, easy-to-use behavioral equivalence that relates terms in $lambda$-calculi by decomposing their normal forms into bisimilar subterms.Moreover, it typically allows for powerful up-to techniques, such as bisimulation up to context, which simplify bisimulation proofs even further.However, proving soundness of these