Perhaps you should try some spelling variations:
"modified df approximation algorithm" » "modified df approximation algorithms", "modified _ approximation algorithm", "modified one approximation algorithm", "modified time approximation algorithm", "modified adam approximation algorithm", "modified bi1 approximation algorithm"
"modified network estimation algorithm" » "modified network optimization algorithm", "certified network estimation algorithm", "defined network estimation algorithm", "modified near estimation algorithm"

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