@article{10_4153_CMB_2008_031_8,
     author = {Witbooi, P. J.},
     title = {Relative {Homotopy} in {Relational} {Structures}},
     journal = {Canadian mathematical bulletin},
     pages = {310--320},
     year = {2008},
     volume = {51},
     number = {2},
     doi = {10.4153/CMB-2008-031-8},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-2008-031-8/}
}