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Examples include the Ramanujan–Nagell equation , " x " , and the equation of the Fermat-Catalan conjecture and Beal 's conjecture , " c " with inequality restrictions on the exponents .
 Ramanujan–Nagell, Fermat-Catalan, Beal
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Ramanujan–Nagell, Fermat-Catalan, Beal