@article{10_2140_agt_2012_12_685,
     author = {Powell, Mark},
     title = {A second order algebraic knot concordance group},
     journal = {Algebraic and Geometric Topology},
     pages = {685--751},
     year = {2012},
     volume = {12},
     number = {2},
     doi = {10.2140/agt.2012.12.685},
     url = {http://geodesic.mathdoc.fr/articles/10.2140/agt.2012.12.685/}
}