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In mathematics , an infrastructure is a group - like structure appearing in global field s. Historic development In 1972 , D. Shanks first discovered the infrastructure of a real quadratic number field and applied his baby-step giant-step algorithm to compute the regulator of such a field in \ mathcal ( D ^ ) binary operations ( for every \ varepsilon > 0 ) , where D is the discriminant of the quadratic field ; previous methods required \ mathcal ( D ^ ) binary operations .
 D. Shanks
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
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Answer:
 D. Shanks