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 notion estimation algorithms" » "modified notion estimation algorithm", "modified notion optimization algorithms", "modified notion optimisation algorithm", "modified motion estimation algorithms"

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