Perhaps you should try some spelling variations:
"modified average approximation algorithm" » "modified average approximation algorithms", "modified coverage approximation algorithm"
"modified objective convolution algorithms" » "modified objective evolution algorithm", "modified objective solution algorithm"

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• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified average approximation algorithm") OR ("modified objective convolution algorithms"))~.
• Removing quotes may allow a broader search: (( modified average approximation algorithm ) or ( modified objective convolution algorithms ))~.
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