@article{MAN_1963__152_161095, author = {H. Wang}, title = {Tag {Systems} and {Lag} {Systems.}}, journal = {Mathematische Annalen}, pages = {65--74}, publisher = {mathdoc}, volume = {152}, year = {1963}, zbl = {0131.24602}, url = {http://geodesic.mathdoc.fr/item/MAN_1963__152_161095/} }