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As of early 2013 , over 200 natural products are known to contain a nitrogen - nitrogen ( N - N ) bond .
 Chemical: nitrogen; Chemical: nitrogen; Chemical: N - N
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: nitrogen; Chemical: nitrogen; Chemical: N - N