Override parallel operators on Empty for optimization.
Optimize iterator() of empty sequence.
Make test clear using Matcher.
Fix issue due to parallel execuction.
Consolidate two SkipEnumerator.
Implement elementAt operator for ParallelSeq that fallback to sequential for now.
Implement orElse operator.
Sophisticate a way of using Ignore annotation.
Separate test helper method.
Implements toArray operator that supports parallel execution.
Fix an issue that parallel operators are not performed in parallel.
Implement orderBy(Descending) operator that is executed in parallel.
Preserve an ordering of source index.
Fix test of which result is indeterministic.
Implements thenBy(Descending) that is executed in parallel.