@article{10_4153_CJM_2008_028_3,
     author = {Hitrik, Michael and Sj\"ostrand, Johannes},
     title = {Non-Selfadjoint {Perturbations} of {Selfadjoint} {Operators} in {Two} {Dimensions} {IIIa.} {One} {Branching} {Point}},
     journal = {Canadian journal of mathematics},
     pages = {572--657},
     year = {2008},
     volume = {60},
     number = {3},
     doi = {10.4153/CJM-2008-028-3},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-2008-028-3/}
}