added class stubs (#20)
added example (#20)
added method stubs (#20)
added test case stub (#20)
added comments (#20)
implemented tests (#20)
fixed test data (#20)
implemented Triple (#20)
added test case stub (#20)
added comments (#20)
implemented tests (#20)
added iterator method stubs (#20)
implemented iterator (#20)
added test (#20)
improved implementation to ensure that the iterator can be reused (#20)
refactoring: extracted methods (#20)
re-organized statements (#20)
added comments (#20)
refactoring: resetting a list requires a key update (#20)
refactoring: resetting a list requires always a reset of the sub-lists (#20)