Distance-preserving maps in generalized polygons. I: Maps on flags. Govaert, Eline; Van Maldeghem, Hendrik — 2002 Beiträge zur Algebra und Geometrie
Distance-preserving maps in generalized polygons. II: Maps on points and/or lines. Govaert, Eline; Van Maldeghem Hendrik — 2002 Beiträge zur Algebra und Geometrie