@article{SF_1986__35_134853,
     author = {J.D. Lawson},
     title = {Fields of tangent sets and {Hofmann} cones.},
     journal = {Semigroup forum},
     pages = {1--28},
     publisher = {mathdoc},
     volume = {35},
     year = {1986},
     zbl = {0619.22007},
     url = {http://geodesic.mathdoc.fr/item/SF_1986__35_134853/}
}