Perhaps you should try some spelling variations:
"generation theorem" » "generation theory", "separation theorem", "preparation theorem"
"operation theory" » "operations theory", "iteration theory", "generation theory"
"operator theory" » "operators theory"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("operator theory") OR ((("operation theory") OR ("generation theorem")))).
• Removing quotes may allow a broader search: (( operator theory ) or ((( operation theory ) or ( generation theorem )))).
• Adding a wildcard symbol may retrieve word variants: (("operator theory") or ((("operation theory") or ("generation theorem"))))*.