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Therefore , the definition of a theorem in system L is : Examples An example of the proof of a sequent ( Modus Tollendo Tollens in this case ) : An example of the proof of a sequent ( a theorem in this case ) : Each rule of system L has its own requirements for the type of input ( s ) or entry ( es ) that it can accept and has its own way of treating and calculating the assumptions used by its inputs .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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