@article{10_2140_agt_2001_1_743,
     author = {Berrick, A J and Davydov, A A},
     title = {Splitting of {Gysin} extensions},
     journal = {Algebraic and Geometric Topology},
     pages = {743--762},
     year = {2001},
     volume = {1},
     number = {2},
     doi = {10.2140/agt.2001.1.743},
     url = {http://geodesic.mathdoc.fr/articles/10.2140/agt.2001.1.743/}
}