go_back, travel_sym(Id), at(FutureLocation)
, history(GrandparentId, LastLocation, ParentId), history(ParentId, Location)
	<=> history(GrandparentId, LastLocation)
      , at(Location)
      , travel_sym(ParentId)

go_back, travel_sym(FutureID), at(FutureLocation), history(Id, Location)
	<=> at(Location)
      , travel_sym(Id)

go_back <=> nowhere_to_go

go_to(NewLocation), at(Location), history(ParentId, LastLocation), travel_sym(Id)
 	<=> history(ParentId, LastLocation, Id), history(Id, Location)
      , at(NewLocation)
	  , travel_sym(Id + 1)
      
 
 go_to(NewLocation), travel_sym(Id), at(Location)
 	<=> history(Id, Location)
      , at(NewLocation)
      , travel_sym(Id + 1)

start <=> at("Home"), travel_sym(0)