Subnormality and 2-hyponormality for Toeplitz operators.
The following problem is studied: is every 2-hyponormal Toeplitz operator subnormal? The answer is negative and there is a gap. The author gives an example of a Toeplitz operator which is 2-hyponormal but not subnormal. The problem about minimal conditions for when a 2-hyponormal Toeplitz operator is subnormal or normal are also discussed.
scientific article; zbMATH DE number 1890574
scientific article