Use factory method instead of constructor.
Implement reverse operator.
Implement indexWhere operator.
Remove ignore annotation.
Split test.
Implement indexOf operator.
Implement lastIndexWhere operator.
Implement lastIndexOf operator.
Correct test.
Implements concat operator.
Implements concat operator that produces ParallelSeq.
Correct javadoc.
Implement toLookup.
Ignore too-slow test.
Refactoring.
Add tests.
Implements toLookup that is executed in parallel.
Correct test.
Add tests.
Remove unnecessary constructor.