@article{SPS_1976__10__216_0,
     author = {Williams, David},
     title = {The {Q-matrix} problem},
     journal = {S\'eminaire de probabilit\'es de Strasbourg},
     pages = {216--234},
     publisher = {Springer - Lecture Notes in Mathematics},
     volume = {10},
     year = {1976},
     mrnumber = {440707},
     zbl = {0361.60035},
     language = {en},
     url = {http://www.numdam.org/item/SPS_1976__10__216_0/}
}