F. Flegel. (2018)cite arxiv:1801.05684Comment: 14 pages. Generalizes the results of article arXiv:1608.02415 to higher order eigenvectors. For better readability, we have copied the main definitions.
R. Cortez, and J. Fontbona. (2015)cite arxiv:1512.09308Comment: 28 pages. This version is accepted for publication in Communications in Mathematical Physics.