From the design.md

Analyzer

Make sure that:

• (essential) add_card uses MapSet.member? and MapSet.put
• (essential) trade_card uses MapSet.member?, MapSet.put and MapSet.delete
• (essential) remove_duplicates uses MapSet.new and Enum.sort
• (essential) remove_duplicates does not use Enum.unique
• (essential) extra_cards uses MapSet.difference and MapSet.size
• (essential) boring_cards uses MapSet.intersection and Enum.sort
• (actionable) boring_cards uses Enum.reduce
• (essential) total_cards uses MapSet.union and MapSet.size
• (actionable) total_cards uses Enum.reduce
• (essential) split_shiny_cards uses MapSet.partition and Enum.sort
• (actionable) split_shiny_cards uses String.startsWith