Giacomo Lenzi. Mu-depth 3 is more than 2: a game-theoretic proof. Mathematical Structures in Computer Science, 11(2):273-297, 2001.
@article{Lenzi01:0, title = {Mu-depth 3 is more than 2: a game-theoretic proof}, author = {Giacomo Lenzi}, year = {2001}, researchr = {https://researchr.org/publication/Lenzi01%3A0}, cites = {0}, citedby = {0}, journal = {Mathematical Structures in Computer Science}, volume = {11}, number = {2}, pages = {273-297}, }