Edelsbrunner, H., O’Rourke, J., &; Welzl, E. (1984). Stationing guards in rectilinear art galleries. Computer Vision, Graphics, and Image Processing. Elsevier.https://doi.org/10.1016/S0734-189X(84)80041-9 
LibreCat: https://research-explorer.ista.ac.at/record/4118
DOI: 10.1016/S0734-189X(84)80041-9