@article{JGG_2014_18_2_JGG_2014_18_2_a6,
     author = {S. Stamatakis and I. Kaffas and I.-I. Papadopoulou },
     title = {Characterizations of {Ruled} {Surfaces} in {R\protect\textsuperscript{3}} and of {Hyperquadrics} in {R\protect\textsuperscript{n+1}} via {Relative} {Geometric} {Invariants}},
     journal = {Journal for geometry and graphics},
     pages = {217--223},
     publisher = {mathdoc},
     volume = {18},
     number = {2},
     year = {2014},
     url = {http://geodesic.mathdoc.fr/item/JGG_2014_18_2_JGG_2014_18_2_a6/}
}