Nominal Unification and Matching of Higher Order Expressions with Recursive Let

A sound and complete algorithm for nominal unification of higher-order expressions with a recursive let is described, shown to run in nondeterministic polynomial time. We also explore specializations like letrec-matching expressions, DAGs, garbage-free determine their complexity. provide atom-variables, where we show that it runs In addition prove there guessing strategy letrec atom-variable trade-off between exponential growth non-determinism. Nominal matching variables representing partial letrec-environments be NP.