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