Finally, the systems' autopoietic closure is another fundamental difference from Parsons' concept. Each system works strictly according to its very own code and can observe other systems only by applying its code to their operations. For example, the code of the economy involves the application of the distinction between payment and non-payment. Other system operations appear within the economic field of references only insofar as this economic code can be applied to them. Hence, a political decision becomes an economic operation when it is observed as a government spending money or not. Likewise, a legal judgement may also be an economic operation when settlement of a contractual dispute obliges one party to pay for the goods or services they had acquired. The codes of the economy, politics and law operate autonomously, but their "interpenetration" is evident when observing "events" which simultaneously involve the participation of more than one system.