%0 Article %A Grätzer George A. %D 2007 %G English %B Acta scientiarum mathematicarum %@ 0001-6969 %T Subdirectly irreducible modular lattices of width at most 4 %U http://acta.bibl.u-szeged.hu/16172/1/math_073_numb_001_002_003-030.pdf