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 optimization algorithms" » "modified network optimisation algorithm", "modified network estimation algorithms", "modified network estimation algorithm", "certified network optimization algorithms", "defined network optimization algorithms", "modified near optimization algorithms"

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