Perhaps you should try some spelling variations:
"generation theory" » "generation theorem", "integration theory", "generation through"
"generative theory" » "generalized theory", "integrative theory", "alternative theory"
"iteration theory" » "integration theory", "interaction theory", "vibration theory"
"generation third" » "generation theorem", "interaction third"
"operator theory" » "operators theory", "operation 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 ((("iteration theory") OR ((((("generation theory") OR ("generation third"))) OR ("generative theory")))))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"operator theory\") or (((\"iteration theory\") or (((((\"generation theory\") OR (\"generation third\"))) or (\"generative theory\"))))))".
• Removing quotes may allow a broader search: (( operator theory ) or ((( iteration theory ) or ((((( generation theory ) OR ( generation third ))) or ( generative theory )))))).
• Adding a wildcard symbol may retrieve word variants: (("operator theory") or ((("iteration theory") or ((((("generation theory") OR ("generation third"))) or ("generative theory"))))))*.