Perhaps you should try some spelling variations:
"varying environments and operational considerations" » "varying environments and computational considerations", "varying environments and additional considerations", "varying environment and operational considerations", "working environments and operational considerations", "changing environments and operational considerations"
"learning environments and operational considerations" » "learning environments and computational considerations", "learning environments and additional considerations"
"varying environments and operational conditions" » "varying environments and operating conditions", "varying environments and operational definitions", "varying environments and operational control", "varying environment and operational conditions", "working environments and operational conditions", "changing 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 conditions") OR ((("varying environments and operational considerations") OR ("learning environments and operational considerations")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"varying environments and operational conditions\") or (((\"varying environments and operational considerations\") OR (\"learning environments and operational considerations\"))))".
• Removing quotes may allow a broader search: (( varying environments and operational conditions ) or ((( varying environments and operational considerations ) OR ( learning environments and operational considerations )))).
• Adding a wildcard symbol may retrieve word variants: (("varying environments and operational conditions") or ((("varying environments and operational considerations") OR ("learning environments and operational considerations"))))*.