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