@unpublished{ Zaspel:2015, author = {P. Zaspel}, title = {{Subspace correction methods in algebraic multi-level frames}}, year = {2015}, pdf = {http://wissrech.ins.uni-bonn.de/research/pub/zaspel/algebraic_frames_ins_preprint.pdf} , month = {june}, note = {INS Preprint No. 1510, submitted to Linear Algebra and its Applications.}, inspreprintnum= {1510} }