Perhaps you should try some spelling variations:
"difference and function relationship" » "difference and function relationships", "difference and function regulationhip", "difference and function relationshipship", "difference and functional relationshiphip"
"difference and function equations" » "difference and functional equations", "difference and functional equation", "difference and reaction equations"
"difference and function relations" » "difference and function regulation", "difference and function relationships", "difference and functional relationship"

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