|context> => |context: prolog travel>

car |auckland> +=> |hamilton>
car |hamilton> +=> |raglan>
car |valmont> +=> |saarbruecken>
car |valmont> +=> |metz>

train |metz> +=> |frankfurt>
train |saarbruecken> +=> |frankfurt>
train |metz> +=> |paris>
train |saarbruecken> +=> |paris>

plane |frankfurt> +=> |bangkok>
plane |frankfurt> +=> |singapore>
plane |paris> +=> |losAngeles>
plane |bangkok> +=> |auckland>
plane |singapore> +=> |auckland>
plane |losAngeles> +=> |auckland>