Perhaps you should try some spelling variations:
approximation algorithm » approximation algorithms
one approximation » time approximation, _ approximation, rough approximations
df estimation » _ estimation
modified one » modified male, modified near, modified orca
modified df » modified _, modified adam, modified bi1

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• Performing a fuzzy search may retrieve terms with similar spellings: (( modified one approximation algorithm ) or ( modified df estimation algorithm ))~.
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