About: http://webisa.webdatacommons.org/182836879

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	U.S. Pat. No. 2,674,332 of Ovshinsky discloses such a system as being attached as an accessory to a vehicle such as a tractor to permit it to be directed back and forth in a series of parallel paths.
http://www.w3.org/ns/prov#wasQuotedFrom	google.ca