#1 Tutorial query causes error return

lookup Line "3" traverse Line:StationOnLine:Member:Station where has_rail end show Station:name, Station:zone

Could not determine key of primary node - query needs a primary expression

lookup Line "3" traverse Line:StationOnLine:Member:Station where has_rail end show name, Station:name, Station:zone

The query: ``` lookup Line "3" traverse Line:StationOnLine:Member:Station where has_rail end show Station:name, Station:zone ``` causes: ``` Could not determine key of primary node - query needs a primary expression ``` changing the query to: ``` lookup Line "3" traverse Line:StationOnLine:Member:Station where has_rail end show name, Station:name, Station:zone ``` works.