Perhaps you should try some spelling variations:
"defined network approximation algorithm" » "defined network approximation algorithms"
"modified network optimization algorithm" » "modified network optimization algorithms", "modified network optimisation algorithm", "modified network estimation algorithm", "certified network optimization algorithm", "modified near optimization algorithm"

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