@article{GT_1999_3_1_a1,
     author = {Roberts, Justin},
     title = {Classical 6j-symbols and the tetrahedron},
     journal = {Geometry & topology},
     pages = {21--66},
     publisher = {mathdoc},
     volume = {3},
     number = {1},
     year = {1999},
     doi = {10.2140/gt.1999.3.21},
     url = {http://geodesic.mathdoc.fr/articles/10.2140/gt.1999.3.21/}
}