Perhaps you should try some spelling variations:
"certified network approximation algorithm" » "certified network approximation algorithms", "verified network approximation algorithm"
"modified parameters estimation algorithm" » "modified parameter estimation algorithm", "modified parameter estimates algorithm", "modified parameter optimization algorithm"

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• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"certified network approximation algorithm\") OR (\"modified parameters estimation algorithm\"))~".
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