Perhaps you should try some spelling variations:
"generation theory" » "generation theorem", "generative theory", "iteration theory"
"operators theory" » "operator theory"
"operation theory" » "operations theory", "operator theory", "iteration 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: (("operators theory") OR ((("operation theory") OR ("generation theory")))).
• Removing quotes may allow a broader search: (( operators theory ) or ((( operation theory ) or ( generation theory )))).
• Adding a wildcard symbol may retrieve word variants: (("operators theory") or ((("operation theory") or ("generation theory"))))*.