Perhaps you should try some spelling variations:
"varying environments and operational definitions" » "varying environments and operational definition", "varying environments and operational decision", "learning environments and operational definitions", "working environments and operational definitions", "changing environments and operational definitions", "making environments and operational definitions"
"varying environment and operational definitions" » "varying environment and operational definition", "varying environment and operational decision", "learning environment and operational definitions", "working environment and operational definitions", "making environment and operational definitions"
"varying environments and operational conditions" » "varying environments and operating conditions", "varying environments and operational considerations", "varying environments and operational control", "learning environments and operational conditions", "working environments and operational conditions", "changing environments and operational conditions", "making environments and operational conditions"

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• If you are trying to use Boolean operators, they must be ALL CAPS: (((("varying environments and operational definitions") OR ("varying environment and operational definitions"))) OR ("varying environments and operational conditions")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"varying environments and operational definitions\") OR (\"varying environment and operational definitions\"))) or (\"varying environments and operational conditions\"))".
• Removing quotes may allow a broader search: (((( varying environments and operational definitions ) OR ( varying environment and operational definitions ))) or ( varying environments and operational conditions )).
• Adding a wildcard symbol may retrieve word variants: (((("varying environments and operational definitions") OR ("varying environment and operational definitions"))) or ("varying environments and operational conditions"))*.