@ARTICLE{g2015a, author = {D. Gallistl}, title = {An optimal adaptive {FEM} for eigenvalue clusters}, journal = {Numer. Math.}, year = {2015}, doi = {10.1007/s00211-014-0671-8}, fjournal = {Numerische Mathematik}, volume = {130}, number = {3}, pages = {467--496}, }