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While these layers address different concerns (displaying information to the user in the outer layer vs. business rules in the inner layer.), we can also distinguish a separation of concern within a single layer. The best example is found in the inner domain layer, in which business rules are placed. Not all rules concern the same topic, and you want them to be decoupled from other rules. This might be an additional layer. You are not limited to three in the number of ayers layers in the clean architecture. You might also develop the rules separately and create communication between the two using an API. Essentially this means that two onions rings are created that together form a working system. This may be represented by one large onion ring that includes the two smaller onions.

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