A Fully Equational Proof of Parikh's Theorem
Luca Aceto, Zoltán Ésik, Anna Ingólfsdóttir · RAIRO - Theoretical Informatics and Applications · 2002
We show that the validity of Parikh's theorem for context-free languages depends only on a few equational properties of least pre-fixed points. Moreover, we exhibit an infinite basis of μ-term equations of continuous commutative idempotent semirings.