@article{DMGAA_2002_22_2_a5,
     author = {Ho{\l}ubowski, Waldemar},
     title = {An inverse matrix of an upper triangular matrix can be lower triangular},
     journal = {Discussiones Mathematicae. General Algebra and Applications},
     pages = {161--166},
     publisher = {mathdoc},
     volume = {22},
     number = {2},
     year = {2002},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/DMGAA_2002_22_2_a5/}
}